[dart2wasm] Support casting to and calling Function

Also fix parameter type of ClassID.getID

These changes are necessary to support the hash implementation changes
in https://dart-review.googlesource.com/c/sdk/+/237582

Change-Id: Ic7448fae647be57a55f9e1d08b3ece780e60fd3b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/240402
Reviewed-by: Joshua Litt <joshualitt@google.com>
Commit-Queue: Aske Simon Christensen <askesc@google.com>

Author: askeksa

pkg/dart2wasm/lib/code_generator.dart

@@ -1660,8 +1660,8 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
   @override
   w.ValueType visitFunctionInvocation(
       FunctionInvocation node, w.ValueType expectedType) {
-    FunctionType functionType = node.functionType!;
-    int parameterCount = functionType.requiredParameterCount;
+    int parameterCount = node.functionType?.requiredParameterCount ??
+        node.arguments.positional.length;
     return _functionCall(parameterCount, node.receiver, node.arguments);
   }
 
@@ -2057,7 +2057,10 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
         .getSubtypesOf(type.classNode)
         .where((c) => !c.isAbstract)
         .toList();
-    if (concrete.isEmpty) {
+    if (type.classNode == translator.coreTypes.functionClass) {
+      ClassInfo functionInfo = translator.classInfo[translator.functionClass]!;
+      translator.ref_test(b, functionInfo);
+    } else if (concrete.isEmpty) {
       b.drop();
       b.i32_const(0);
     } else if (concrete.length == 1) {

sdk/lib/_internal/wasm/lib/class_id.dart

@@ -6,7 +6,7 @@
 
 @pragma("wasm:entry-point")
 class ClassID {
-  external static int getID(Object value);
+  external static int getID(Object? value);
 
   @pragma("wasm:class-id", "dart.typed_data#_ExternalUint8Array")
   external static int get cidExternalUint8Array;