Fix regular expression construction

[HalidOdat]

The previous implementation used the global RegExp, which caused errors when the RegExp was overwritten.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	95,574	95,574	0
Passed	75,201	75,201	0
Ignored	19,482	19,482	0
Failed	891	891	0
Panics	0	0	0
Conformance	78.68%	78.68%	0.00%

[codecov]

Codecov Report

Attention: 25 lines in your changes are missing coverage. Please review.

Comparison is base (e54609e) 49.42% compared to head (b7a16aa) 49.45%.
Report is 3 commits behind head on main.

❗ Current head b7a16aa differs from pull request most recent head 01fa079. Consider uploading reports for the commit 01fa079 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3338      +/-   ##
==========================================
+ Coverage   49.42%   49.45%   +0.03%     
==========================================
  Files         445      446       +1     
  Lines       43891    43948      +57     
==========================================
+ Hits        21691    21733      +42     
- Misses      22200    22215      +15     

Files	Coverage Δ
boa_engine/src/bytecompiler/expression/mod.rs	58.21% <100.00%> (+1.63%)	⬆️
boa_engine/src/vm/opcode/mod.rs	5.32% <ø> (ø)
boa_ast/src/expression/mod.rs	62.96% <66.66%> (+0.08%)	⬆️
boa_engine/src/vm/flowgraph/mod.rs	0.00% <0.00%> (ø)
boa_parser/src/parser/expression/primary/mod.rs	54.38% <50.00%> (+0.05%)	⬆️
boa_ast/src/visitor.rs	20.87% <0.00%> (-0.21%)	⬇️
boa_ast/src/expression/regexp.rs	76.47% <76.47%> (ø)
boa_engine/src/vm/code_block.rs	51.55% <0.00%> (-0.52%)	⬇️
boa_engine/src/vm/opcode/push/literal.rs	64.51% <54.54%> (-12.41%)	⬇️

... and 10 files with indirect coverage changes

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[jedel1043]

Nice fix! Some small nitpicks that don't block merging.

[nekevss]

Nice work 😄