Implement support of Symbol.toPrimitive

[tofpie]

This Pull Request implements the use of Symbol.toPrimitive in the to_primitive method of Value.

It changes the following:

• to_primitive method of Value to support Symbol.toPrimitive

[codecov]

Codecov Report

Merging #1020 (219e1ae) into master (3b83767) will increase coverage by 0.01%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master    #1020      +/-   ##
==========================================
+ Coverage   60.10%   60.12%   +0.01%     
==========================================
  Files         167      167              
  Lines       11142    11152      +10     
==========================================
+ Hits         6697     6705       +8     
- Misses       4445     4447       +2     

Impacted Files	Coverage Δ
boa/src/value/mod.rs	73.95% <60.00%> (-0.38%)	⬇️
boa/src/object/gcobject.rs	66.55% <0.00%> (+0.68%)	⬆️

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[Razican]

The conformance improvement looks nice :)

Test262 conformance changes:

Test result	master count	PR count	difference
Total	78,493	78,493	0
Passed	20,882	20,942	+60
Ignored	15,585	15,585	0
Failed	42,026	41,966	-60
Panics	388	388	0
Conformance	26.60	26.68	+0.08%

[Razican]

Thanks!