perf(ext/fetch): skip USVString webidl conv on string constructor (#12168)
* perf(ext/fetch): skip USVString webidl conv on string constructor
* Rename webidl convert to RequestInfo_DOMString
To disambiguate and hint that it normalizes to DOMString instead of USVString since DOMString => USVString is handled by `op_url_parse` when calling `new URL(...)`