Implement and document PEP 669.

[markshannon]

Now that PEP 669 is accepted, it needs to be implemented and documented.

• Implement the PEP
• Decide on and implement policy for monitors seeing the code in other monitors.
• Document the PEP
• Use "macro" instructions to reduce code duplication in bytecodes.c

Linked PRs

• GH-103082: Implementation of PEP 669: Low Impact Monitoring for CPython #103083
• GH-103082: Code cleanup from review. #103474
• GH-103082: Turn on branch events for FOR_ITER instructions. #103507
• gh-103082: Fix shifted field initialization in instrumentation.c #103561
• GH-103082: Filter LINE events in VM, to simplify tool implementation. #104387
• GH-103082: Rename PY_MONITORING_EVENTS to _PY_MONITORING_EVENTS #107069
• [3.12] GH-103082: Rename PY_MONITORING_EVENTS to _PY_MONITORING_EVENTS (#107069) #107075
• GH-103082: Document PEP-669: Low Impact Monitoring for CPython #107772
• gh-103082: use IS_VALID_OPCODE instead of _PyOpcode_OpName to check if an opcode is defined #107882
• gh-103082: remove assumption that INSTRUMENTED_LINE is the last instrumented opcode #107978
• [3.12] GH-103082: Document PEP-669: Low Impact Monitoring for CPython (GH-107772) #108909
• [3.12] GH-103082: Clean up the sys.monitoring docs #111048

[markshannon]

Also needs to be added to the "What's new" and the PEP needs to be marked as accepted/final.

[markshannon]

Specific things to document (that aren't clear from the PEP) (from comments by @gvanrossum):

event_set is a "set" constructed by OR-ing various events together (a common C idiom of course but not apparent until you see their integer values).

From GVR: "The naming of the CALL and RETURN/RAISE events is a bit confusing -- we have CALL (universal), C_RETURN/PY_RETURN (per language), but then C_RAISE and RAISE -- why isn't the latter PY_RAISE, just for consistency?"

There are good reasons for this design, so they should be documented.

[pablogsal]

Seems that this PR (#103083) has broken the tracerefs buildbot:

https://buildbot.python.org/all/#/builders/484/builds/3091