[std] Improve string hashing

[MaxGraey]

Benchmark:

old str hash: 221.40000015497208 ms
new str hash: 186.04000005871058 ms

playground

• I've read the contributing guidelines

[MaxGraey]

Also I think better migrate to XXHash32: https://github.com/Cyan4973/xxHash

[dcodeIO]

Yeah, FNV was meant as an easy way to get this going, but isn't necessarily the most efficient. Would expect to replace it eventually anyway, but should remain reasonably small.

[MaxGraey]

Closing in favour of #1580