Fix how type parameters are collected from parametrized `Protocol` bases

[brianschubert]

Fixes #636, backport of https://github.com/python/cpython/pull/137281

Added some inline comments about the implementation below.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 94.50549% with 5 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 97.30%. Comparing base (4f42e6b) to head (d748b5d). :warning: Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/typing_extensions.py	92.64%	5 Missing :warning:

@@            Coverage Diff             @@
##             main     #667      +/-   ##
==========================================
- Coverage   97.36%   97.30%   -0.07%     
==========================================
  Files           3        3              
  Lines        7680     7768      +88     
==========================================
+ Hits         7478     7559      +81     
- Misses        202      209       +7     

Flag	Coverage Δ
3.10	?
3.10.4	88.65% <57.14%> (-0.34%)	:arrow_down:
3.11	?
3.11.0	87.13% <60.43%> (-0.33%)	:arrow_down:
3.12	87.84% <60.43%> (-0.33%)	:arrow_down:
3.12.0	?
3.13	?
3.13.0	?
3.14	79.10% <61.53%> (+0.27%)	:arrow_up:
3.9	89.35% <56.04%> (-0.36%)	:arrow_down:
3.9.12	89.35% <56.04%> (-0.36%)	:arrow_down:
pypy3.10	88.49% <57.14%> (-0.34%)	:arrow_down:
pypy3.11	87.75% <60.43%> (-0.33%)	:arrow_down:
pypy3.9	89.18% <56.04%> (-0.36%)	:arrow_down:

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Files with missing lines	Coverage Δ
src/test_typing_extensions.py	98.36% <100.00%> (-0.03%)	:arrow_down:
src/typing_extensions.py	93.82% <92.64%> (-0.06%)	:arrow_down:

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