Part of#95913Forward port of#93306, which was a backport of#93185, to address#84694This adds the What's New entry for the removal of the subinterpreter-related env variable, build-time flag, etc. As@ericsnowcurrently  was author of the original changes, I added him as a co-author to the commit.This addition to the Python 3.11 What's New document were only made to the Python 3.11 branch during the backport process, and not added to the version in `main`. Forward-porting it ensures the docs retain these additions for the future, rather than being lost in a legacy Python versions, allows it to be be edited as part of#95913 , and avoids merge conflicts with routine back-ports of PRs touching it.I've pulled in the addition exactly as-is with no modifications; any editing will be done in future PRs (and therefore can be reviewed and backported accordingly).The one other such addition is forward-ported in#98344

* main: (31 commits)pythongh-95913: Move subinterpreter exper removal to 3.11 WhatsNew (pythonGH-98345)pythongh-95914: Add What's New item describing PEP 670 changes (python#98315)  Remove unused arrange_output_buffer function from zlibmodule.c. (pythonGH-98358)pythongh-98174: Handle EPROTOTYPE under macOS in test_sendfile_fallback_close_peer_in_the_middle_of_receiving (python#98316)pythonGH-98327: Reduce scope of catch_warnings() in _make_subprocess_transport (python#98333)pythongh-93691: Compiler's code-gen passes location around instead of holding it on the global compiler state (pythonGH-98001)pythongh-97669: Create Tools/build/ directory (python#97963)pythongh-95534: Improve gzip reading speed by 10% (python#97664)pythongh-95913: Forward-port int/str security change to 3.11 What's New in main (python#98344)pythonGH-91415: Mention alphabetical sort ordering in the Sorting HOWTO (pythonGH-98336)pythongh-97930: Merge with importlib_resources 5.9 (pythonGH-97929)pythongh-85525: Remove extra row in doc (python#98337)pythongh-85299: Add note warning about entry point guard for asyncio example (python#93457)pythongh-97527: IDLE - fix buggy macosx patch (python#98313)pythongh-98307: Add docstring and documentation for SysLogHandler.createSocket (pythonGH-98319)pythongh-94808: Cover `PyFunction_GetCode`, `PyFunction_GetGlobals`, `PyFunction_GetModule` (python#98158)pythonGH-94597: Deprecate child watcher getters and setters (python#98215)pythongh-98254: Include stdlib module names in error messages for NameErrors (python#98255)  Improve speed. Reduce auxiliary memory to 16.6% of the main array. (pythonGH-98294)  [doc] Update logging cookbook with an example of custom handling of levels. (pythonGH-98290)  ...