Make precompile and can_precompile not take self

[jprendes]

This PR makes it so that precompile and can_precompile do not take self.

The main intention is that ideally we would not need an engine to precompile.
If a runtime can precompile without instantiating the wasm runtime, that would be ideal.

This would allow us to move all engine creation inside of the zygote process.

This makes tests a bit more finicky, as configuring the fake engine is not as simple.

However, the non-test code changes are rather straight forward.

This is marked as draft as I'm still exploring options.

[jprendes]

@jsturtevant , what do you think of doing something like this?

My main complain is that it makes the engine precompilation kind of a "global" thing.

Maybe an "EngineBuilder" would be a better idea, and we can move the precompilation to the engine builder.