url: prioritize toString when stringifying

The ES addition operator calls the ToPrimitive() abstract operation
without hint String, leading a subsequent OrdinaryToPrimitive() to call
valueOf() first on an object rather than the desired toString().

Instead, use template literals which directly call ToString() abstract
operation, per Web IDL spec.

PR-URL: https://github.com/nodejs/node/pull/11737
Fixes: b610a4db "url: enforce valid UTF-8 in WHATWG parser"
Refs: https://github.com/nodejs/node/commit/b610a4db1c2919f88711962f5797f25ecb1cd36b#commitcomment-21200056
Refs: https://tc39.github.io/ecma262/#sec-addition-operator-plus-runtime-semantics-evaluation
Refs: https://tc39.github.io/ecma262/#sec-template-literals-runtime-semantics-evaluation


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>