Fix reflection-calling Set method on arrays (dotnet#107529)

The test added in dotnet#106787 found an issue in the implementation of reflection calls to array `Set` methods. We used to throw the wrong exception type. There were probably other corner case bugs (like what exception is thrown when both element type is wrong and index is out of range and when/how value coercion should happen). This should fix that.

src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Augments/RuntimeAugments.cs

@@ -120,6 +120,32 @@ public static unsafe Array NewMultiDimArray(RuntimeTypeHandle typeHandleForArray
  return Array.NewMultiDimArray(typeHandleForArrayType.ToMethodTable(), pImmutableLengths, lengths.Length);
  }
 
+ public static unsafe void SetArrayValue(Array array, int[] indices, object value)
+ {
+ MethodTable* elementMT = array.ElementMethodTable;
+
+ if (elementMT->IsPointer || elementMT->IsFunctionPointer)
+ {
+ Debug.Assert(value.GetMethodTable()->ValueTypeSize == IntPtr.Size);
+ elementMT = value.GetMethodTable();
+ }
+
+ if (elementMT->IsValueType)
+ {
+ Debug.Assert(value.GetMethodTable()->IsValueType && elementMT->ValueTypeSize == value.GetMethodTable()->ValueTypeSize);
+ nint flattenedIndex = array.GetFlattenedIndex(indices);
+ ref byte element = ref Unsafe.AddByteOffset(ref MemoryMarshal.GetArrayDataReference(array), (nuint)flattenedIndex * array.ElementSize);
+ RuntimeImports.RhUnbox(value, ref element, elementMT);
+ }
+ else
+ {
+ RuntimeImports.RhCheckArrayStore(array, value);
+ nint flattenedIndex = array.GetFlattenedIndex(indices);
+ ref object element = ref Unsafe.Add(ref Unsafe.As<byte, object>(ref MemoryMarshal.GetArrayDataReference(array)), flattenedIndex);
+ element = value;
+ }
+ }
+
  public static IntPtr GetAllocateObjectHelperForType(RuntimeTypeHandle type)
  {
  return RuntimeImports.RhGetRuntimeHelperForType(type.ToMethodTable(), RuntimeHelperKind.AllocateObject);

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Array.NativeAot.cs

@@ -727,7 +727,7 @@ private unsafe nint GetFlattenedIndex(int rawIndex)
  return rawIndex;
  }
 
- private unsafe nint GetFlattenedIndex(ReadOnlySpan<int> indices)
+ internal unsafe nint GetFlattenedIndex(ReadOnlySpan<int> indices)
  {
  // Checked by the caller
  Debug.Assert(indices.Length == Rank);

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeArrayTypeInfo.cs

@@ -213,7 +213,7 @@ internal sealed override IEnumerable<RuntimeMethodInfo> SyntheticMethods
  for (int i = 0; i < rank; i++)
  indices[i] = (int)(args[i]);
  object value = args[rank];
- array.SetValue(value, indices);
+ RuntimeAugments.SetArrayValue(array, indices, value);
  return null;
  }
  );