Optimize number to PropertyKey conversion

[HalidOdat]

In previous implementation when converting a number to PropertyKey, we always converted it to string and only when the conversion to PropertyKey::Index was not possible we returned that string.

Instead of using map_or which expects a ready value we use the _else version that takes a function. Also took the oportunity to optimize the i32 to PropertyKey conversion, since it's the one that's called when we convert from JsValue::Integer. Additionaly added a static string for "length" for internal array methods so we don't convert from &[u16] to PropertyKey.

Because the conversion happens very often this change resulted in big performance improvements :)

Benchmarks

Main

PROGRESS Richards
RESULT Richards 57.0
PROGRESS DeltaBlue
RESULT DeltaBlue 61.6
PROGRESS Encrypt
PROGRESS Decrypt
RESULT Crypto 62.7
PROGRESS RayTrace
RESULT RayTrace 188
PROGRESS Earley
PROGRESS Boyer
RESULT EarleyBoyer 176
PROGRESS Splay
RESULT Splay 185
PROGRESS NavierStokes
RESULT NavierStokes 117
SCORE 107

PR

PROGRESS Richards
RESULT Richards 58.8
PROGRESS DeltaBlue
RESULT DeltaBlue 63.7
PROGRESS Encrypt
PROGRESS Decrypt
RESULT Crypto 71.7
PROGRESS RayTrace
RESULT RayTrace 198
PROGRESS Earley
PROGRESS Boyer
RESULT EarleyBoyer 182
PROGRESS Splay
RESULT Splay 193
PROGRESS NavierStokes
RESULT NavierStokes 158
SCORE 117

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	50,268	50,268	0
Passed	42,773	42,773	0
Ignored	1,391	1,391	0
Failed	6,104	6,104	0
Panics	18	18	0
Conformance	85.09%	85.09%	0.00%

[raskad]

Really nice find!

[nekevss]

Nice work!