Caching obj_callp invocations

[fwsGonzo]

Right now obj_callp invocations are slower than when using GDScript very likely because GDScript caches the object-method combination. We should be doing the same, similar to what godot-cpp does.

It's not obvious how to cache an obj-callp call: How do you get a unique class identifier? How do you get a unique method identifier? I suppose the method can be just a hash, but the class? Also a hash?

Even with all these pre-requisites lined up, how do you look up the method call, before calling it?

[fwsGonzo]

It may be easier to do this with the run-time generated API, as it provides us the means to use hashes on both sides to communicate these known calls.

[fwsGonzo]

One idea here is to modify the guest variants to match the expected arguments, but handle the data as untrusted and verify it based on that. After that it makes sense to ship that to the known function with the expected arguments.

Not sure if enough scrunity.