Implement Array.prototype.reduce

[benjaminflin]

I implemented Array.prototype.reduce according to the spec. Let me know if I missed anything as this is my first time contributing.

[codecov]

Codecov Report

Merging #555 into master will increase coverage by 1.65%.
The diff coverage is 89.65%.

@@            Coverage Diff             @@
##           master     #555      +/-   ##
==========================================
+ Coverage   68.19%   69.84%   +1.65%     
==========================================
  Files         172      172              
  Lines       10573    10796     +223     
==========================================
+ Hits         7210     7541     +331     
+ Misses       3363     3255     -108     

Impacted Files	Coverage Δ
boa/src/builtins/array/mod.rs	80.97% <83.78%> (+0.16%)	⬆️
boa/src/builtins/array/tests.rs	100.00% <100.00%> (ø)
boa/src/exec/tests.rs	100.00% <0.00%> (ø)
boa/src/builtins/math/tests.rs	100.00% <0.00%> (ø)
boa/src/builtins/bigint/tests.rs	100.00% <0.00%> (ø)
boa/src/builtins/number/tests.rs	100.00% <0.00%> (ø)
boa/src/builtins/object/tests.rs	100.00% <0.00%> (ø)
boa/src/syntax/lexer/mod.rs	56.09% <0.00%> (+0.24%)	⬆️
boa/src/builtins/value/operations.rs	30.87% <0.00%> (+0.46%)	⬆️
boa/src/builtins/object/internal_methods.rs	30.36% <0.00%> (+0.52%)	⬆️
... and 41 more

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[HalidOdat]

Looks good! check my comments on how to improve it :)

[HalidOdat]

Perfect! Thanks for the contribution @benjaminflin :)

[Razican]

Looks very good, thanks! Could you check the second TypeError message? Also, I would prefer if we added some tests for the error cases too.