Add ROSpan Equals/CompareTo/IndexOf/Contains string-like APIs with StringComparison (#27319)

* Add ROSpan Equals/CompareTo/IndexOf/Contains string-like APIs with StringComparison

* Respond to recent change AsReadOnlySpan -> AsSpan

* Remove the out parameter from IndexOf

* Add tests and avoid allocations for StringComparison.Ordinal

* Remove duplicate definition of SoftHyphen

Author: ahsonkhan

src/System.Memory/System.Memory.sln

@@ -27,6 +27,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "ref", "ref", "{2E666815-2ED
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{3F794AE4-319F-4498-A9DA-C49A4EB11D9E}"
 	ProjectSection(SolutionItems) = preProject
+		..\Common\src\CoreLib\System\Runtime\InteropServices\MemoryMarshal.Fast.cs = ..\Common\src\CoreLib\System\Runtime\InteropServices\MemoryMarshal.Fast.cs
 		..\Common\src\CoreLib\System\ReadOnlySpan.Fast.cs = ..\Common\src\CoreLib\System\ReadOnlySpan.Fast.cs
 		..\Common\src\CoreLib\System\Span.Fast.cs = ..\Common\src\CoreLib\System\Span.Fast.cs
 		..\Common\src\CoreLib\System\Span.NonGeneric.cs = ..\Common\src\CoreLib\System\Span.NonGeneric.cs

src/System.Memory/ref/System.Memory.cs

@@ -29,11 +29,15 @@ public static partial class MemoryExtensions
         public static int BinarySearch<T, TComparable>(this System.ReadOnlySpan<T> span, TComparable comparable) where TComparable : System.IComparable<T> { throw null; }
         public static int BinarySearch<T, TComparer>(this System.Span<T> span, T value, TComparer comparer) where TComparer : System.Collections.Generic.IComparer<T> { throw null; }
         public static int BinarySearch<T, TComparable>(this System.Span<T> span, TComparable comparable) where TComparable : System.IComparable<T> { throw null; }
+        public static int CompareTo(this System.ReadOnlySpan<char> span, System.ReadOnlySpan<char> value, System.StringComparison comparisonType) { throw null; }
+        public static bool Contains(this System.ReadOnlySpan<char> span, System.ReadOnlySpan<char> value, System.StringComparison comparisonType) { throw null; }
         public static void CopyTo<T>(this T[] array, System.Memory<T> destination) { }
         public static void CopyTo<T>(this T[] array, System.Span<T> destination) { }
         public static bool EndsWith(this System.ReadOnlySpan<char> span, System.ReadOnlySpan<char> value, System.StringComparison comparisonType) { throw null; }
         public static bool EndsWith<T>(this System.ReadOnlySpan<T> span, System.ReadOnlySpan<T> value) where T : System.IEquatable<T> { throw null; }
         public static bool EndsWith<T>(this System.Span<T> span, System.ReadOnlySpan<T> value) where T : System.IEquatable<T> { throw null; }
+        public static bool Equals(this System.ReadOnlySpan<char> span, System.ReadOnlySpan<char> value, System.StringComparison comparisonType) { throw null; }
+        public static int IndexOf(this System.ReadOnlySpan<char> span, System.ReadOnlySpan<char> value, System.StringComparison comparisonType) { throw null; }
         public static int IndexOfAny<T>(this System.ReadOnlySpan<T> span, System.ReadOnlySpan<T> values) where T : System.IEquatable<T> { throw null; }
         public static int IndexOfAny<T>(this System.ReadOnlySpan<T> span, T value0, T value1) where T : System.IEquatable<T> { throw null; }
         public static int IndexOfAny<T>(this System.ReadOnlySpan<T> span, T value0, T value1, T value2) where T : System.IEquatable<T> { throw null; }

src/System.Memory/src/System/MemoryExtensions.Portable.cs

@@ -13,6 +13,58 @@ namespace System
     /// </summary>
     public static partial class MemoryExtensions
     {
+        /// <summary>
+        /// Returns a value indicating whether the specified <paramref name="value"/> occurs within the <paramref name="span"/>.
+        /// <param name="span">The source span.</param>
+        /// <param name="value">The value to seek within the source span.</param>
+        /// <param name="comparisonType">One of the enumeration values that determines how the <paramref name="span"/> and <paramref name="value"/> are compared.</param>
+        /// </summary>
+        public static bool Contains(this ReadOnlySpan<char> span, ReadOnlySpan<char> value, StringComparison comparisonType)
+            => (IndexOf(span, value, comparisonType) >= 0);
+
+        /// <summary>
+        /// Determines whether this <paramref name="span"/> and the specified <paramref name="value"/> span have the same characters
+        /// when compared using the specified <paramref name="comparisonType"/> option.
+        /// <param name="span">The source span.</param>
+        /// <param name="value">The value to compare with the source span.</param>
+        /// <param name="comparisonType">One of the enumeration values that determines how the <paramref name="span"/> and <paramref name="value"/> are compared.</param>
+        /// </summary>
+        public static bool Equals(this ReadOnlySpan<char> span, ReadOnlySpan<char> value, StringComparison comparisonType)
+        {
+            if (comparisonType == StringComparison.Ordinal)
+            {
+                return span.SequenceEqual<char>(value);
+            }
+
+            return span.ToString().Equals(value.ToString(), comparisonType);
+        }
+
+        /// <summary>
+        /// Compares the specified <paramref name="span"/> and <paramref name="value"/> using the specified <paramref name="comparisonType"/>,
+        /// and returns an integer that indicates their relative position in the sort order.
+        /// <param name="span">The source span.</param>
+        /// <param name="value">The value to compare with the source span.</param>
+        /// <param name="comparisonType">One of the enumeration values that determines how the <paramref name="span"/> and <paramref name="value"/> are compared.</param>
+        /// </summary>
+        public static int CompareTo(this ReadOnlySpan<char> span, ReadOnlySpan<char> value, StringComparison comparisonType) 
+            => string.Compare(span.ToString(), value.ToString(), comparisonType);
+        
+        /// <summary>
+        /// Reports the zero-based index of the first occurrence of the specified <paramref name="value"/> in the current <paramref name="span"/>.
+        /// <param name="span">The source span.</param>
+        /// <param name="value">The value to seek within the source span.</param>
+        /// <param name="comparisonType">One of the enumeration values that determines how the <paramref name="span"/> and <paramref name="value"/> are compared.</param>
+        /// </summary>
+        public static int IndexOf(this ReadOnlySpan<char> span, ReadOnlySpan<char> value, StringComparison comparisonType)
+        {
+            if (comparisonType == StringComparison.Ordinal)
+            {
+                return span.IndexOf<char>(value);
+            }
+
+            return span.ToString().IndexOf(value.ToString(), comparisonType);
+        }
+        
         /// <summary>
         /// Copies the characters from the source span into the destination, converting each character to lowercase,
         /// using the casing rules of the specified culture.