Adding new API that accepts resusable context.

[jakubDoka]

Sadly due to how the code was structured, I needed to change the `Env' fields so basically everything that was used was changed as well. I did not benchmark anything yet (work in progress).

Context -> https://bytecodealliance.zulipchat.com/#narrow/stream/217117-cranelift/topic/Using.20context.20for.20.60TargetIsa.3A.3Acompile_function.60