chore(Worklets): merge isSynchronizable impl (#9027)

## Summary

After giving it some thought I decided that it makes no sense to provide
a throwing implementation for `isSynchronizable` on web if
`createSynchronizable` already throws.

A bit of DRY to the codebase.

## Test plan

🚀

Author: tjzel

packages/react-native-worklets/src/memory/isSynchronizable.native.ts

@@ -1,10 +1,14 @@
 'use strict';
 
-import { WorkletsError } from '../debug/WorkletsError';
 import type { Synchronizable } from './types';
 
 export function isSynchronizable<TValue>(
-  _value: unknown
-): _value is Synchronizable<TValue> {
-  throw new WorkletsError('`isSynchronizable` is not supported on web.');
+  value: unknown
+): value is Synchronizable<TValue> {
+  'worklet';
+  return (
+    typeof value === 'object' &&
+    value !== null &&
+    !!(value as Record<string, unknown>).__synchronizableRef
+  );
 }