Add workaround to IMethodSymbolExtensions.RenameTypeParameters

This makes the extension method work again. The workaround is tracked by
https://github.com/dotnet/roslyn/issues/36093.

src/Workspaces/Core/Portable/Shared/Extensions/IMethodSymbolExtensions.cs

@@ -86,7 +86,8 @@ public static IMethodSymbol RenameTypeParameters(this IMethodSymbol method, ILis
             var updatedTypeParameters = RenameTypeParameters(
                 method.TypeParameters, newNames, typeGenerator);
 
-            var mapping = new Dictionary<ITypeSymbol, ITypeSymbol>();
+            // The use of AllNullabilityIgnoringSymbolComparer is tracked by https://github.com/dotnet/roslyn/issues/36093
+            var mapping = new Dictionary<ITypeSymbol, ITypeSymbol>(AllNullabilityIgnoringSymbolComparer.Instance);
             for (int i = 0; i < method.TypeParameters.Length; i++)
             {
                 mapping[method.TypeParameters[i]] = updatedTypeParameters[i];
@@ -139,7 +140,9 @@ public static IMethodSymbol RenameTypeParameters(this IMethodSymbol method, ILis
             // We generate the type parameter in two passes.  The first creates the new type
             // parameter.  The second updates the constraints to point at this new type parameter.
             var newTypeParameters = new List<CodeGenerationTypeParameterSymbol>();
-            var mapping = new Dictionary<ITypeSymbol, ITypeSymbol>();
+
+            // The use of AllNullabilityIgnoringSymbolComparer is tracked by https://github.com/dotnet/roslyn/issues/36093
+            var mapping = new Dictionary<ITypeSymbol, ITypeSymbol>(AllNullabilityIgnoringSymbolComparer.Instance);
             for (int i = 0; i < typeParameters.Length; i++)
             {
                 var typeParameter = typeParameters[i];