Separate declarative environment kinds

[jedel1043]

This Pull Request separates declarative environments into kinds, which makes it easier to add more kinds in the future (spoiler: module environments).

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	94,657	94,657	0
Passed	73,889	73,889	0
Ignored	17,505	17,505	0
Failed	3,263	3,263	0
Panics	0	0	0
Conformance	78.06%	78.06%	0.00%

[codecov]

Codecov Report

Merging #2921 (8926dba) into main (85a253e) will increase coverage by 0.08%.
The diff coverage is 87.16%.

@@            Coverage Diff             @@
##             main    #2921      +/-   ##
==========================================
+ Coverage   51.98%   52.06%   +0.08%     
==========================================
  Files         431      435       +4     
  Lines       43647    43689      +42     
==========================================
+ Hits        22690    22748      +58     
+ Misses      20957    20941      -16     

Impacted Files	Coverage Δ
boa_engine/src/builtins/function/mod.rs	39.74% <ø> (ø)
boa_engine/src/builtins/generator/mod.rs	31.84% <ø> (ø)
boa_engine/src/vm/opcode/push/new_target.rs	0.00% <0.00%> (ø)
boa_engine/src/builtins/function/arguments.rs	96.61% <50.00%> (+0.84%)	⬆️
boa_engine/src/vm/opcode/environment/mod.rs	53.53% <64.00%> (+2.35%)	⬆️
...e/src/environments/runtime/declarative/function.rs	77.77% <77.77%> (ø)
boa_engine/src/vm/code_block.rs	56.57% <88.23%> (ø)
boa_engine/src/environments/runtime/mod.rs	79.62% <92.75%> (ø)
...engine/src/environments/runtime/declarative/mod.rs	93.67% <93.67%> (ø)
boa_engine/src/builtins/eval/mod.rs	64.21% <100.00%> (-1.79%)	⬇️
... and 5 more

[raskad]

Really nice refactor! This makes the runtime environment code much more readable. Great work.

[HalidOdat]

Nice refactor! :)