Make boa::parse emit error on invalid input, not panic

[gorogoroumaru]

This Pull Request fixes/closes #772 .

It changes the following:

• boa::parse panics on invalid input. This behavior is not expected, and I fixed this to emit error on invalid input
• fixed typo in boa/src/syntax/ast/op.rs

[codecov]

Codecov Report

Merging #807 into master will increase coverage by 0.14%.
The diff coverage is 61.10%.

@@            Coverage Diff             @@
##           master     #807      +/-   ##
==========================================
+ Coverage   59.15%   59.29%   +0.14%     
==========================================
  Files         155      165      +10     
  Lines        9841    10320     +479     
==========================================
+ Hits         5821     6119     +298     
- Misses       4020     4201     +181     

Impacted Files	Coverage Δ
boa/src/builtins/console/mod.rs	22.47% <ø> (+3.37%)	⬆️
boa/src/builtins/string/string_iterator.rs	77.50% <0.00%> (ø)
boa/src/environment/global_environment_record.rs	27.95% <0.00%> (ø)
boa/src/lib.rs	86.36% <ø> (ø)
boa/src/object/iter.rs	21.21% <ø> (ø)
boa/src/profiler.rs	0.00% <0.00%> (ø)
boa/src/property/attribute/mod.rs	86.95% <ø> (-3.67%)	⬇️
boa/src/syntax/ast/node/await_expr/mod.rs	0.00% <0.00%> (ø)
boa/src/syntax/ast/op.rs	11.23% <ø> (ø)
boa/src/syntax/parser/expression/await_expr.rs	0.00% <0.00%> (ø)
... and 96 more

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[gorogoroumaru]

Thank you @Lan2u and @HalidOdat!
I applied your suggested changes.