gh-105481: opcode.h is no longer generated during the build

[iritkatriel]

Python's operators don't change very often. This doesn't need to be auto-generated.

• Issue: Generate opcode metadata from bytecodes.c instead of opcode.py #105481

[gvanrossum]

LG, though I'm unsure of the benefit here. We now have two places where the list of NB_ constants occurs, once in opcode.h, once in _opcode.c, and they must be kept in sync manually.

[gvanrossum]

I dislike marking the "last" of anything, you end up doing + 1 in various places. But I realize that it's a convention around opcode definitions and the like.

[iritkatriel]

There are a number of lists/enumerations that need to exist in parallel python and C. I think to avoid the duplication in the code we should design something generic that spawns the #definitions in C and a function that builds the python dict to map the name to the number. Something like argument clinic, but for enumerations. I don't like having a special script for each case.