Update SYSLIB0012 obsoletion messages to be clear and consistent (#41483)

Co-authored-by: Jeff Handley <jeff.handley@microsoft.com>

Author: github-actions[bot]

docs/project/list-of-obsoletions.md

@@ -24,4 +24,4 @@ Currently the identifiers `SYSLIB0001` through `SYSLIB0999` are carved out for o
 |  __`SYSLIB0009`__ | The AuthenticationManager Authenticate and PreAuthenticate methods are not supported and throw PlatformNotSupportedException. |
 |  __`SYSLIB0010`__ | This Remoting API is not supported and throws PlatformNotSupportedException. |
 |  __`SYSLIB0011`__ | `BinaryFormatter` serialization is obsolete and should not be used. See https://aka.ms/binaryformatter for recommended alternatives. |
-|  __`SYSLIB0012`__ | Use Location instead. |
+|  __`SYSLIB0012`__ | Assembly.CodeBase and Assembly.EscapedCodeBase are only included for .NET Framework compatibility. Use Assembly.Location instead. |

src/libraries/Common/src/System/Obsoletions.cs

@@ -40,7 +40,7 @@ internal static class Obsoletions
         internal const string BinaryFormatterMessage = "BinaryFormatter serialization is obsolete and should not be used. See https://aka.ms/binaryformatter for more information.";
         internal const string BinaryFormatterDiagId = "SYSLIB0011";
 
-        internal const string CodeBaseMessage = "Use Location instead.";
+        internal const string CodeBaseMessage = "Assembly.CodeBase and Assembly.EscapedCodeBase are only included for .NET Framework compatibility. Use Assembly.Location instead.";
         internal const string CodeBaseDiagId = "SYSLIB0012";
     }
 }

src/libraries/System.Reflection.Emit/ref/System.Reflection.Emit.cs

@@ -9,7 +9,7 @@ namespace System.Reflection.Emit
     public sealed partial class AssemblyBuilder : System.Reflection.Assembly
     {
         internal AssemblyBuilder() { }
-        [System.ObsoleteAttribute("CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.", DiagnosticId = "SYSLIB0012", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
+        [System.ObsoleteAttribute("Assembly.CodeBase and Assembly.EscapedCodeBase are only included for .NET Framework compatibility. Use Assembly.Location instead.", DiagnosticId = "SYSLIB0012", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
         public override string? CodeBase { get { throw null; } }
         public override System.Reflection.MethodInfo? EntryPoint { get { throw null; } }
         public override string? FullName { get { throw null; } }

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -7585,12 +7585,12 @@ public AmbiguousMatchException(string? message, System.Exception? inner) { }
     public abstract partial class Assembly : System.Reflection.ICustomAttributeProvider, System.Runtime.Serialization.ISerializable
     {
         protected Assembly() { }
-        [System.ObsoleteAttribute("CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.", DiagnosticId = "SYSLIB0012", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
+        [System.ObsoleteAttribute("Assembly.CodeBase and Assembly.EscapedCodeBase are only included for .NET Framework compatibility. Use Assembly.Location instead.", DiagnosticId = "SYSLIB0012", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
         public virtual string? CodeBase { get { throw null; } }
         public virtual System.Collections.Generic.IEnumerable<System.Reflection.CustomAttributeData> CustomAttributes { get { throw null; } }
         public virtual System.Collections.Generic.IEnumerable<System.Reflection.TypeInfo> DefinedTypes { [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types might be removed")] get { throw null; } }
         public virtual System.Reflection.MethodInfo? EntryPoint { get { throw null; } }
-        [System.ObsoleteAttribute("CodeBase and EscapedCodeBase are only included for .NET Framework compatibility. Use Location instead.", DiagnosticId = "SYSLIB0012", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
+        [System.ObsoleteAttribute("Assembly.CodeBase and Assembly.EscapedCodeBase are only included for .NET Framework compatibility. Use Assembly.Location instead.", DiagnosticId = "SYSLIB0012", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
         public virtual string EscapedCodeBase { get { throw null; } }
         public virtual System.Collections.Generic.IEnumerable<System.Type> ExportedTypes { [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Types might be removed")] get { throw null; } }
         public virtual string? FullName { get { throw null; } }