Replace slow std functions with native built-ins

[moleike]

We are using the exact same Jsonnet implementation of the std object that is used in the C++ original implementation
This replacement would not need to modify the vanilla std.jsonnet since we can override them in the native impl.

This should heavily rely on micro-benchmarks so that we only re-implement methods that are known to be slow.

Methods:

• std.join in 5cb1201
• https://jsonnet.org/ref/stdlib.html