feat(tbx): handle extended metadata in tbx format

[amCap1712]

Handle TermWeb extended metadata: 'definition', 'Translation needed', 'administrativeStatus' and 'Usage note' in accordance with #12795. The _get_notes_list method is reimplemented in TBXUnit based on translate toolkit's tbxunit.getnotes to appropriately filter the extended metadata terms based on node tag and attributes.

I was a bit perplexed by the reference files attached in the the issue. They were multilingual files and it took me a while to realize that weblate doesn't support importing multilingual files (only mono or bi). Further, the TBX format (at least some versions if not all) support multiple terms inside termEntry tag, in these cases Weblate only considers the first term tag. Please correct me if my understanding is wrong.

The administrativeStatus and Translation needed seem general enough to upstream the support in Translate Toolkit. Thoughts?

[codecov]

Codecov Report

❌ Patch coverage is 96.07843% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.16%. Comparing base (845c499) to head (7adde90).
⚠️ Report is 2623 commits behind head on main.

Files with missing lines	Patch %	Lines
weblate/formats/ttkit.py	93.54%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14998   +/-   ##
=======================================
  Coverage   91.15%   91.16%           
=======================================
  Files         626      626           
  Lines       65459    65513   +54     
  Branches     6751     6759    +8     
=======================================
+ Hits        59672    59724   +52     
  Misses       4059     4059           
- Partials     1728     1730    +2     

Files with missing lines	Coverage Δ
weblate/formats/tests/test_formats.py	99.78% <100.00%> (+<0.01%)	⬆️
weblate/formats/ttkit.py	91.22% <93.54%> (+0.15%)	⬆️

... and 3 files with indirect coverage changes

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[nijel]

Indeed pushing that to translate-toolkit seems reasonable. For the various comments, it could be also implemented there, the getnotes has origin parmeter to distinguish different kinds.

[amCap1712]

translate/translate#5601. For comments, explanation does not seem to be a unit field in translate-tooklit.

[nijel]

https://github.com/translate/translate/releases/tag/3.15.3 is out with the changes, you can now base on that after adjusting the minimal required version.

[nijel]

Merged, thanks for your contribution!