feat(engine): add JsUint8Array::to_vec for copying viewed bytes

[alienx5499]

This Pull Request fixes/closes #4722.

It changes the following:

• Add SliceRef::to_vec() helper to copy buffer data (including AtomicSlice) into Vec<u8>
• Add JsUint8Array::to_vec(&mut Context) to copy the viewed byte range of a JsUint8Array into a Vec<u8>
• Add a small round-trip test (uint8_array_to_vec_roundtrip) and a doc example for JsUint8Array::to_vec

Testing:

• cargo test -p boa_engine (including the new unit test and doctest)

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	49,687	49,687	0
Ignored	2,262	2,262	0
Failed	1,014	1,014	0
Panics	0	0	0
Conformance	93.81%	93.81%	0.00%

Tested main commit: 34ca7f1f404c2712d6897c3e39e5f5e981ce9ed6
Tested PR commit: eeab895384fb3f692b208674c8a00b0b8b74c2e7
Compare commits: 34ca7f1...eeab895

[alienx5499]

Hi @jedel1043,
I’d appreciate a review when you get time.