fix: URLSearchParams.forEach() crash and spec compliance (#327)

- Use v8::Undefined(isolate) instead of empty v8::Local<v8::Value>()
- Changed argument order from (key, value) to (value, key, searchParams)
- Use get_entries() iterator instead of get_keys() + get() for duplicate keys
- Support the optional thisArg second parameter

Author: adrian-niculescu