🐞 Add underscore to encodeURIComponent skipped characters

[Vectorized]

Description

Not a big issue, as escaping underscores will still work tho.
Just not faithful to the JavaScript implementation.

Checklist

Ensure you completed all of the steps below before submitting your pull request:

• Ran forge fmt?
• Ran forge test?

Pull requests with an incomplete checklist will be thrown out.

[github-actions]

Gas Snapshot Comparison Report

Generated at commit : b3ba66e, Compared to commit : b43371a

Contract Name	Test Name	Main Gas	PR Gas	Diff
LibStringTest	testStringEncodeURIComponent()	19245	20352	1107
	testStringEscapeJSONHexEncode()	709115	710023	908
	testStringPackAndUnpackOne()	737456	738627	1171
	testStringPackAndUnpackTwo()	895109	1076843	181734
	testToStringPositiveNumberBrutalized()	586828	587735	907
	testToStringUint256MaxBrutalized()	598361	599237	876
	testToStringZeroBrutalized()	586333	587208	875
	test__codesize()	46318	46357	39

[atarpara]

@Vectorized LGTM!