Read file input in bytes instead of string

[jevancc]

This Pull Request is a follow-up PR for #915, which closes #876.

This PR may also improve run-time performance slightly since it removes the unnecessary bytes to utf8 chars conversion when reading the files.

It changes the following:

• Read the file input in bytes (boa_cli)

Except for file input in boa_cli, all the other places still take input in str and convert it to bytes afterward:

boa_cli command prompt

The crate rustyline reads input in strings and takes care of it.

boa_wasm

wasm_bindgen makes JS interface and takes input in strings.

test/benchmark

The benchmark still uses include_str! to read the bench scripts. Since the files are read in compile-time, it does not affect the run-time performance. Keep it as it can also benefit because it checks if there are any invalid chars in the bench scripts in compile time.
Similar reasons for tests. Taking the input in str makes the tests simpler and clearer.

[codecov]

Codecov Report

Merging #979 (345baee) into master (b058b2d) will increase coverage by 0.10%.
The diff coverage is 65.21%.

@@            Coverage Diff             @@
##           master     #979      +/-   ##
==========================================
+ Coverage   59.56%   59.67%   +0.10%     
==========================================
  Files         166      166              
  Lines       10815    10807       -8     
==========================================
+ Hits         6442     6449       +7     
+ Misses       4373     4358      -15     

Impacted Files	Coverage Δ
boa_cli/src/main.rs	33.33% <ø> (ø)
boa_tester/src/exec.rs	0.00% <0.00%> (ø)
boa/src/context.rs	61.43% <100.00%> (+0.17%)	⬆️
boa/src/lib.rs	88.46% <100.00%> (+2.09%)	⬆️
...ntax/parser/expression/left_hand_side/arguments.rs	63.15% <0.00%> (+5.26%)	⬆️
...tax/parser/expression/assignment/exponentiation.rs	94.44% <0.00%> (+9.44%)	⬆️
boa/src/syntax/parser/expression/mod.rs	92.53% <0.00%> (+14.05%)	⬆️

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[Razican]

Thanks!