Docs: make htmllive: open browser when ready

[hugovk]

Like python/peps#3558 and python/devguide#1233.

When running make -C Docs htmllive, this will open the browser when the docs have been built the first time.

It means you don't need to hunt around for the link in:

❯ make -C Doc htmllivemkdir -p buildBuilding NEWS from Misc/NEWS.d with blurb./venv/bin/sphinx-autobuild -b html -d build/doctrees -j auto --re-ignore="/venv/" --open-browser --delay 0 -W . build/html[sphinx-autobuild] > sphinx-build -b html -d build/doctrees -j auto -W /Users/hugo/github/python/cpython/main/Doc /Users/hugo/github/python/cpython/main/Doc/build/htmlRunning Sphinx v6.2.1loading pickled environment... donebuilding [mo]: targets for 0 po files that are out of datewriting output...building [html]: targets for 463 source files that are out of dateupdating environment: 0 added, 4 changed, 0 removedreading sources... [100%] whatsnew/changeloglooking for now-outdated files... none foundpickling environment... donechecking consistency... donepreparing documents... donewriting output... [100%] whatsnew/2.2 .. whatsnew/indexgenerating indices... genindex py-modindex donewriting additional pages... download index search opensearch donecopying images... [100%] using/win_installer.pngcopying downloadable files... [100%] includes/tzinfo_examples.pycopying static files... donecopying extra files... donedumping search index in English (code: en)... donedumping object inventory... doneWriting glossary.jsonbuild succeeded.The HTML pages are in build/html.[I 231219 15:20:27 server:335] Serving on http://127.0.0.1:8000[I 231219 15:20:27 handlers:62] Start watching changes[I 231219 15:20:27 handlers:64] Start detecting changes[I 231219 15:20:28 handlers:135] Browser Connected: http://127.0.0.1:8000/

Also make ALLSPHINXOPTS multiline to match https://github.com/python/devguide/blob/78fc0d7aa9fd0d6733d10c23b178b2a0e2799afc/Makefile#L18-L23 and https://github.com/python/peps/blob/9779c7efe63ab8dbb8bb673c5346c35505d97065/Makefile#L14-L17 to make it much easier to compare and maintain them.

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📚 Documentation preview 📚: https://cpython-previews--113288.org.readthedocs.build/

[miss-islington-app]

Thanks @hugovk for the PR 🌮🎉.. I'm working now to backport this PR to: 3.11, 3.12.
🐍🍒⛏🤖

[bedevere-app]

GH-113484 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-113485 is a backport of this pull request to the 3.11 branch.