Implement Well-Known Symbols

[joshwd36]

This Pull Request closes #585.

It changes the following:

• Moves create_intrinsics from Realm to Interpreter
• Changes the signature of the init function from pub(crate) fn init(global: &Value) -> (&str, Value) to pub(crate) fn init(interpreter: &mut Interpreter) -> (&'static str, Value), allowing the init functions to reference the interpreter
• Add the Well-Known Symbols to the Symbol object

[codecov]

Codecov Report

Merging #587 into master will increase coverage by 0.15%.
The diff coverage is 96.51%.

@@            Coverage Diff             @@
##           master     #587      +/-   ##
==========================================
+ Coverage   71.10%   71.25%   +0.15%     
==========================================
  Files         177      176       -1     
  Lines       11420    11557     +137     
==========================================
+ Hits         8120     8235     +115     
- Misses       3300     3322      +22     

Impacted Files	Coverage Δ
boa/src/builtins/string/mod.rs	42.81% <ø> (-0.20%)	⬇️
boa/src/realm.rs	70.58% <ø> (+8.08%)	⬆️
boa/src/exec/mod.rs	70.79% <71.42%> (+0.56%)	⬆️
boa/src/builtins/mod.rs	23.33% <83.33%> (+2.64%)	⬆️
boa/src/builtins/array/mod.rs	80.70% <100.00%> (+0.04%)	⬆️
boa/src/builtins/bigint/mod.rs	70.00% <100.00%> (+0.50%)	⬆️
boa/src/builtins/boolean/mod.rs	36.66% <100.00%> (+2.18%)	⬆️
boa/src/builtins/console/mod.rs	29.82% <100.00%> (+0.41%)	⬆️
boa/src/builtins/error/mod.rs	36.36% <100.00%> (+3.03%)	⬆️
boa/src/builtins/error/range.rs	77.27% <100.00%> (+1.08%)	⬆️
... and 38 more

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[HalidOdat]

Looks great :)