ILMarshaler Refactor (dotnet#21227)

* Add support for fields to ILStubMarshalHome objects.

* Make the specific code streams in the ILMarshaler private members.

* Make home members private.

* Move the IL code stream members back to being protected for the marshalers that override EmitMarshalArgumentCLRToNative instead of EmitMarshalArgumentContents/Space.

* Convert virtual specifiers in overrides to override specifiers.

* Remove unused and undefined member.

* Cleanup a few missed virtual/override specifiers.

* Refactor setup methods. Refactor some of the overrides to duplicate less code.

* Refactor the setup stream and add some comments around how the ArgumentOverride/ReturnOverride marshalling system works.

* Use the cleanup work list in SafeHandle marshalling since the work list is now implemented entirely in managed code.

* Generalize DelegateCleanupWorkListElement -> KeepAliveCleanupWorkListElement and rename the managed entry point to match.

* Refactor direct usage of the cleanup code stream in non-overridden marshalers to use the cleanup work list instead.

* Refactor AsAny marshalling to fit into the regular ILMarshaler code-paths.

* Move ILArgIteratorMarshaler over to the full ILMarshaler infrastructure.

* Port ILBlittablePtrMarshaler over to not directly reference m_pcsMarshal.

* Make the specific code streams private and have ILNativeArrayMarshaler fetch the one it needs from the NDirectStubLinker.

* Devirtualize a method on ILMarshaler.

* Fix broken metasig

* Revert "Use the cleanup work list in SafeHandle marshalling since the work list is now implemented entirely in managed code."

This reverts commit aedcdfb.

* Fix ILArgIteratorMarshaler.

* Take 2 on using the cleanup work list for SafeHandles

* Remove unused field

* SafeHandleMarshaler doesn't need to have extra cleanup code when using the CleanupWorkList.

* Move the rest of the SafeHandle marshalling into ArgumentOverride.

* Moved Pinned Native Array special case into an ArgumentOverride.

* Devirtualize

* Remove invalid field hometype.

* Make ILMarshaler::m_pslNDirect private.

* Native Array marshalling fixes.

* Fix STLOC->LDLOC mistakes.

* Add override hook to allow a marshaler to request that byval contents are always converted to native even when not marked as In (i.e. explicitly marked only as Out). Used in AsAny for byval arrays.

* PR Feedback.

* Add explicit pinning path to ilmarshalers.

* Move implementation of ILNativeArrayMarshaler::CanMarshalViaPinning to ilmarshalers.cpp.

* Add missing override specifier.

* Don't create a managed marshaler if we are able to marshal via pinning. Remove extraneous checks against pinning.

* Convert ILWSTRMarshaler to use the MarshalViaPinning functions for its pinning fast-path.

* Enable LPWSTR marshalling to fall back to allocating on the heap for large strings when stack-allocating for native space (byref in-only semantics).

* PR Feedback.

src/System.Private.CoreLib/src/System/StubHelpers.cs

@@ -1485,21 +1485,21 @@ public static void AddToCleanupList(ref CleanupWorkListElement list, CleanupWork
         }
     }
 
-    // Keeps a Delegate instance alive across the full Managed->Native call.
+    // Keeps an object instance alive across the full Managed->Native call.
     // This ensures that users don't have to call GC.KeepAlive after passing a struct or class
     // that has a delegate field to native code.
-    internal sealed class DelegateCleanupWorkListElement : CleanupWorkListElement
+    internal sealed class KeepAliveCleanupWorkListElement : CleanupWorkListElement
     {
-        public DelegateCleanupWorkListElement(Delegate del)
+        public KeepAliveCleanupWorkListElement(object obj)
         {
-            m_del = del;
+            m_obj = obj;
         }
 
-        private Delegate m_del;
+        private object m_obj;
 
         protected override void DestroyCore()
         {
-            GC.KeepAlive(m_del);
+            GC.KeepAlive(m_obj);
         }
     }
 
@@ -1562,9 +1562,9 @@ internal static IntPtr AddToCleanupList(ref CleanupWorkListElement pCleanupWorkL
             return element.AddRef();
         }
 
-        internal static void AddToCleanupList(ref CleanupWorkListElement pCleanupWorkList, Delegate del)
+        internal static void KeepAliveViaCleanupList(ref CleanupWorkListElement pCleanupWorkList, object obj)
         {
-            DelegateCleanupWorkListElement element = new DelegateCleanupWorkListElement(del);
+            KeepAliveCleanupWorkListElement element = new KeepAliveCleanupWorkListElement(obj);
             CleanupWorkListElement.AddToCleanupList(ref pCleanupWorkList, element);
         }
 

src/vm/fieldmarshaler.cpp

@@ -3064,7 +3064,7 @@ VOID FieldMarshaler_Delegate::UpdateNativeImpl(OBJECTREF* pCLRValue, LPVOID pNat
     if (*pCLRValue != NULL && ppCleanupWorkListOnStack != NULL)
     {
         // Call StubHelpers.AddToCleanupList to ensure the delegate is kept alive across the full native call.
-        MethodDescCallSite AddToCleanupList(METHOD__STUBHELPERS__ADD_TO_CLEANUP_LIST_DELEGATE);
+        MethodDescCallSite AddToCleanupList(METHOD__STUBHELPERS__KEEP_ALIVE_VIA_CLEANUP_LIST);
 
         ARG_SLOT args[] =
         {