gh-131421: Fix ASDL kw_defaults being expr* instead of expr?* (+ fix docs ASDL highlighting)

[Demonstrandum]

According to the docs:

(https://docs.python.org/3.15/library/ast.html#ast.arguments)
kw_defaults is a list of default values for keyword-only arguments. If one is None, the corresponding argument is required.

However, ASDL's description of kw_defaults is that it simply a expr*, and not a expr?* as stated by the docs.

This continues the same correction for expr Dict in the ASDL in PR #131419.

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I also corrected the syntax highlighting regex to support the chained qualifiers syntax introduced to the ASDL.

before	after

• Issue: Wrong Python.asdl type for keys in Dict literals #131421

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📚 Documentation preview 📚: https://cpython-previews--133773.org.readthedocs.build/

[picnixz]

We'll just backport this to 3.14 (it'd be really weird to have the first part in 3.14 but not this one)

[Demonstrandum]

any way I can help getting this done?

[serhiy-storchaka]

LGTM. 👍

[miss-islington-app]

Thanks @Demonstrandum for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-143269 is a backport of this pull request to the 3.14 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Arch Linux Usan Function 3.14 (no tier) has failed when building commit 6583951.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1702/builds/188) and take a look at the build logs.
4. Check if the failure is related to this commit (6583951) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1702/builds/188

Failed tests:

• test_urllib2net

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 23, done.        
remote: Counting objects:   5% (1/18)        
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remote: Counting objects: 100% (18/18), done.        
remote: Compressing objects:  20% (1/5)        
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remote: Compressing objects: 100% (5/5)        
remote: Compressing objects: 100% (5/5), done.        
remote: Total 23 (delta 13), reused 13 (delta 13), pack-reused 5 (from 3)        
From https://github.com/python/cpython
 * branch                    3.14       -> FETCH_HEAD
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Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 6583951e7de [3.14] gh-131421: Fix ASDL kw_defaults being `expr*` instead of `expr?*` (GH-133773) (GH-143269)
Switched to and reset branch '3.14'

make: *** [Makefile:2496: buildbottest] Error 2