Lazy evaluation for cooked template string

[jevancc]

This Pull Request makes the evaluation of cooked template strings lazily, which improves the performance in some cases and fixes invalid escapes in raw template strings. The following sample is now supported

function hello(s) { 
    return s.raw; 
}

hello`\u\x`;

It changes the following:

• Add struct TemplateString and update template related keywords
• Update tests
• Fix bug: `use strict`; can not be used to invoke strict mode

[codecov]

Codecov Report

Merging #1103 (2c2ab77) into master (038acb4) will increase coverage by 0.02%.
The diff coverage is 71.92%.

@@            Coverage Diff             @@
##           master    #1103      +/-   ##
==========================================
+ Coverage   58.81%   58.83%   +0.02%     
==========================================
  Files         176      176              
  Lines       12467    12468       +1     
==========================================
+ Hits         7332     7336       +4     
+ Misses       5135     5132       -3     

Impacted Files	Coverage Δ
boa/src/syntax/parser/function/mod.rs	65.15% <0.00%> (+1.91%)	⬆️
boa/src/syntax/parser/expression/primary/mod.rs	69.84% <42.85%> (-3.05%)	⬇️
boa/src/syntax/lexer/token.rs	51.61% <66.66%> (-1.52%)	⬇️
boa/src/syntax/ast/node/template/mod.rs	55.00% <75.00%> (-0.18%)	⬇️
boa/src/syntax/lexer/template.rs	62.74% <75.00%> (+4.41%)	⬆️
...yntax/parser/expression/left_hand_side/template.rs	71.42% <83.33%> (ø)
...c/syntax/parser/expression/primary/template/mod.rs	79.31% <100.00%> (+8.34%)	⬆️
boa/src/syntax/parser/mod.rs	53.84% <100.00%> (+0.27%)	⬆️

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[tofpie]

Looks good to me! Thanks!

[HalidOdat]

Looks good to me! :)