[Merged by Bors] - RegExp constructor should call IsRegExp()

[HalidOdat]

Make the RegExp constructor call the IsRegExp function to check, not just internal slot check.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	94,593	94,593	0
Passed	73,200	73,214	+14
Ignored	17,532	17,532	0
Failed	3,861	3,847	-14
Panics	0	0	0
Conformance	77.38%	77.40%	+0.01%

Fixed tests (14):

test/annexB/built-ins/RegExp/prototype/Symbol.split/Symbol.match-getter-recompiles-source.js [strict mode] (previously Failed)
test/annexB/built-ins/RegExp/prototype/Symbol.split/Symbol.match-getter-recompiles-source.js (previously Failed)
test/built-ins/RegExp/call_with_non_regexp_same_constructor.js [strict mode] (previously Failed)
test/built-ins/RegExp/call_with_non_regexp_same_constructor.js (previously Failed)
test/built-ins/RegExp/from-regexp-like-short-circuit.js [strict mode] (previously Failed)
test/built-ins/RegExp/from-regexp-like-short-circuit.js (previously Failed)
test/built-ins/RegExp/from-regexp-like-get-ctor-err.js [strict mode] (previously Failed)
test/built-ins/RegExp/from-regexp-like-get-ctor-err.js (previously Failed)
test/built-ins/RegExp/call_with_regexp_match_falsy.js [strict mode] (previously Failed)
test/built-ins/RegExp/call_with_regexp_match_falsy.js (previously Failed)
test/built-ins/RegExp/prototype/Symbol.matchAll/isregexp-called-once.js [strict mode] (previously Failed)
test/built-ins/RegExp/prototype/Symbol.matchAll/isregexp-called-once.js (previously Failed)
test/built-ins/RegExp/prototype/Symbol.matchAll/isregexp-this-throws.js [strict mode] (previously Failed)
test/built-ins/RegExp/prototype/Symbol.matchAll/isregexp-this-throws.js (previously Failed)

[codecov]

Codecov Report

Merging #2881 (a11052f) into main (c738b50) will decrease coverage by 0.02%.
The diff coverage is 61.76%.

@@            Coverage Diff             @@
##             main    #2881      +/-   ##
==========================================
- Coverage   51.24%   51.23%   -0.02%     
==========================================
  Files         427      427              
  Lines       42522    42517       -5     
==========================================
- Hits        21790    21783       -7     
- Misses      20732    20734       +2     

Impacted Files	Coverage Δ
boa_engine/src/builtins/string/mod.rs	57.81% <46.66%> (-0.21%)	⬇️
boa_engine/src/builtins/regexp/mod.rs	63.69% <73.68%> (-0.38%)	⬇️

[raskad]

bors r+

[bors]

Pull request successfully merged into main.

Build succeeded:

• Build and Test (macos-latest)
• Build and Test (windows-latest)
• Coverage
• Misc