feat(xml/unstable): add XML 1.1 support

[tomas-zijdemans]

I went for no version auto-detection from  <?xml version="...">. Users explicitly set xmlVersion: "1.1". The reasoning for this is that it's very very common to encounter XML files where the version is not honest, so It would just confuse users. The alternative would be a opaque strict or lenient mode.

I checked XML 1.1
conformance against the official XML test suite.

The XML module gets improved test coverage with this PR

[codecov]

Codecov Report

❌ Patch coverage is 91.40271% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.37%. Comparing base (260f5b8) to head (fe9a1c9).

Files with missing lines	Patch %	Lines
xml/_tokenizer.ts	87.65%	3 Missing and 7 partials ⚠️
xml/_parse_sync.ts	90.90%	0 Missing and 7 partials ⚠️
xml/_entities.ts	80.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7057      +/-   ##
==========================================
- Coverage   94.38%   94.37%   -0.02%     
==========================================
  Files         628      628              
  Lines       50175    50219      +44     
  Branches     8840     8863      +23     
==========================================
+ Hits        47357    47393      +36     
+ Misses       2251     2249       -2     
- Partials      567      577      +10     

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