[Master-Merge Idea] Generate Engine functions

[chippmann]

Currently when a user wants to use the _ready function he has to name the function correctly in order to be used properly for the engine to recognize it:

@RegisterFunction
fun _ready(){}

instead of:

@RegisterFunction
fun ready(){}

more problematic is IMHO the _physics_process function:

@RegisterFunction
fun _physics_process(){}

instead of:

@RegisterFunction
fun physicsProcess(){}

I propose we implement those functions inside the binding that the user can override:

override fun physicsProcess() {}

which would have the other benefit that the user would not have to register engine functions as we could check for them in the entryGeneration.

[chippmann]

This is the case now