Consistently report unresolved members in illink (#103667)

The resolution cache is shared between `Resolve` and
`TryResolve`, so we should call `ReportUnresolved` from `Resolve`
when we see a cached null result (that could have been cached
during `TryResolve`). Should make no difference to supported
scenarios because we always run with `IgnoreUnresolved` `true`.

This was regressed in
dotnet/linker#2253.

---------

Co-authored-by: Jackson Schuster <[email protected]>

Author: sbomer

src/tools/illink/src/linker/Linker/LinkContext.cs

@@ -802,8 +802,11 @@ public int GetTargetRuntimeVersion ()
 			if (methodReference is null)
 				return null;
 
-			if (methodresolveCache.TryGetValue (methodReference, out MethodDefinition? md))
+			if (methodresolveCache.TryGetValue (methodReference, out MethodDefinition? md)) {
+				if (md == null && !IgnoreUnresolved)
+					ReportUnresolved (methodReference);
 				return md;
+			}
 
 #pragma warning disable RS0030 // Cecil's resolve is banned -- this provides the wrapper
 			md = methodReference.Resolve ();
@@ -847,8 +850,11 @@ public int GetTargetRuntimeVersion ()
 			if (fieldReference is null)
 				return null;
 
-			if (fieldresolveCache.TryGetValue (fieldReference, out FieldDefinition? fd))
+			if (fieldresolveCache.TryGetValue (fieldReference, out FieldDefinition? fd)) {
+				if (fd == null && !IgnoreUnresolved)
+					ReportUnresolved (fieldReference);
 				return fd;
+			}
 
 			fd = fieldReference.Resolve ();
 			if (fd == null && !IgnoreUnresolved)
@@ -888,8 +894,11 @@ public int GetTargetRuntimeVersion ()
 			if (typeReference is null)
 				return null;
 
-			if (typeresolveCache.TryGetValue (typeReference, out TypeDefinition? td))
+			if (typeresolveCache.TryGetValue (typeReference, out TypeDefinition? td)) {
+				if (td == null && !IgnoreUnresolved)
+					ReportUnresolved (typeReference);
 				return td;
+			}
 
 			//
 			// Types which never have TypeDefinition or can have ambiguous definition should not be passed in