Generate single interface dispatch map per canonical form (dotnet#76362)

The dispatch maps are identical because canonically-equivalent types have the same vtable layouts.

Author: MichalStrehovsky

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/ConstructedEETypeNode.cs

@@ -38,7 +38,8 @@ protected override DependencyList ComputeNonRelocationBasedDependencies(NodeFact
 
             if (MightHaveInterfaceDispatchMap(factory))
             {
-                dependencyList.Add(factory.InterfaceDispatchMap(_type), "Interface dispatch map");
+                TypeDesc canonType = _type.ConvertToCanonForm(CanonicalFormKind.Specific);
+                dependencyList.Add(factory.InterfaceDispatchMap(canonType), "Interface dispatch map");
             }
 
             if (_type.IsArray)

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/EETypeNode.cs

@@ -1056,7 +1056,8 @@ protected internal virtual void ComputeOptionalEETypeFields(NodeFactory factory,
         {
             if (!relocsOnly && MightHaveInterfaceDispatchMap(factory))
             {
-                _optionalFieldsBuilder.SetFieldValue(EETypeOptionalFieldTag.DispatchMap, checked((uint)factory.InterfaceDispatchMapIndirection(Type).IndexFromBeginningOfArray));
+                TypeDesc canonType = _type.ConvertToCanonForm(CanonicalFormKind.Specific);
+                _optionalFieldsBuilder.SetFieldValue(EETypeOptionalFieldTag.DispatchMap, checked((uint)factory.InterfaceDispatchMapIndirection(canonType).IndexFromBeginningOfArray));
             }
 
             ComputeRareFlags(factory, relocsOnly);

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/InterfaceDispatchMapNode.cs

@@ -22,6 +22,7 @@ public InterfaceDispatchMapNode(NodeFactory factory, TypeDesc type)
             // Pointer arrays also follow the same path
             Debug.Assert(!type.IsArrayTypeWithoutGenericInterfaces());
             Debug.Assert(MightHaveInterfaceDispatchMap(type, factory));
+            Debug.Assert(type.ConvertToCanonForm(CanonicalFormKind.Specific) == type);
 
             _type = type;
         }