Adds a RETURN_GENERATOR bytecode which makes a generator (or coroutine) from the current frame.
This has a number of advantages:

1. Generator frames cannot be incomplete, as the frame is fully initialized before creating the generator
2. It simplifies the code for calling a Python function, as there is no need for a special case for generator functions.
3. It removes the need to specialize calls to generator functions, they can be specialized as any other call to a Python function.

This PR also adds a JUMP_NO_INTERRUPT bytecode. This is the same as JUMP_ABSOLUTE without any checks for interrupts. Checking for interrupts in yield from would destroy the flaky pretense that Python coroutines are stackful. (They are not, but PEPs 380 and 489 like to pretend that they are), so we need the extra, seemingly redundant instruction.

We use RETURN_GENERATOR rather than MAKE_GENERATOR; RETURN_VALUE as the RETURN_VALUE would make the compiler treat all the following code as unreachable. We could fix that using artificial instructions, but I think that is best left to another PR.

https://bugs.python.org/issue46409