Delay instantiation of signature return type

`getReturnTypeOfSignature` correctly handles an un-instantiated
signature, but `instantiateSignature` used to eagerly instantiate the
return type. This caused an infinite recursion in #16233.

Now `instantiateSignature` doesn't instantiate the return type, but
relies on `getReturnTypeOfSignature` to do it.

Author: sandersn

src/compiler/checker.ts

@@ -8038,7 +8038,7 @@ namespace ts {
             const result = createSignature(signature.declaration, freshTypeParameters,
                 signature.thisParameter && instantiateSymbol(signature.thisParameter, mapper),
                 instantiateList(signature.parameters, mapper, instantiateSymbol),
-                instantiateType(signature.resolvedReturnType, mapper),
+                /*resolvedReturnType*/ undefined,
                 freshTypePredicate,
                 signature.minArgumentCount, signature.hasRestParameter, signature.hasLiteralTypes);
             result.target = signature;