JsValue from primitives

[lastmjs]

This Pull Request fixes/closes #1994 and #1991 and depends on #1971.

It changes the following:

• Adds many primitive conversions, From for JsValue where T are integers
• Makes some opinions about i128, u128, i64, and u64 when converting to JsValue, always converting to BigInt

[jedel1043]

This change reduces our conformance by a very large amount. The reason is the conversion for i64, IIRC.

The range of an integer index in javascript is, surprisingly, [0 to 2^53), which is the max integer that is representable by an f64 without loss of precision. When we parse an integer, we use i32 to store it for performance reasons, and fallback to f64 in case the integer exceeds the max value of an i32, because converting from f64 to u64 is faster than converting from JsBigInt to u64.
However, eagerly converting it to JsBigInt automatically makes it unusable as an integer index, and it's instead converted to a string key. This unfortunately breaks indexing for big integer values.

[codecov]

Codecov Report

Merging #1993 (39e2799) into main (6baf455) will decrease coverage by 0.03%.
The diff coverage is 3.33%.

@@            Coverage Diff             @@
##             main    #1993      +/-   ##
==========================================
- Coverage   45.89%   45.85%   -0.04%     
==========================================
  Files         206      206              
  Lines       17150    17170      +20     
==========================================
+ Hits         7871     7874       +3     
- Misses       9279     9296      +17     

Impacted Files	Coverage Δ
boa_engine/src/bigint.rs	37.95% <0.00%> (-1.15%)	⬇️
boa_engine/src/value/mod.rs	51.09% <0.00%> (-0.76%)	⬇️
boa_engine/src/value/conversions.rs	19.64% <4.54%> (-5.36%)	⬇️
boa_engine/src/builtins/string/mod.rs	62.74% <0.00%> (+0.21%)	⬆️
...ine/src/syntax/parser/expression/assignment/mod.rs	30.84% <0.00%> (+1.86%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6baf455...39e2799. Read the comment docs.

[raskad]

Looks good!

[Razican]

As already mentioned in multiple comments, I don't think it's the way forward. This already silently heap-allocates with a TON of overhead many Rust stack primitives. you can already do these conversions explicitly, and there are talks for adding easier boilerplating with a trait and maybe some derives.

[lastmjs]

I'm going to close this pull request in response to the comments.