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:

• [X] std.join in 5cb1201e2fa6ca748d7bec8ede83e991e5b54800
• [ ] https://jsonnet.org/ref/stdlib.html