core: use closure to parse bare id in affine expr parsing

[superlopuh]

PR 1/2 of adding the necessary parsing infrastructure to be able to express affine.vector_load/store (#5365).

[codecov]

Codecov Report

❌ Patch coverage is 87.17949% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.87%. Comparing base (6b63574) to head (0890457).
⚠️ Report is 177 commits behind head on main.

Files with missing lines	Patch %	Lines
xdsl/parser/affine_parser.py	87.17%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5464   +/-   ##
=======================================
  Coverage   85.87%   85.87%           
=======================================
  Files         382      382           
  Lines       54899    54911   +12     
  Branches     6320     6321    +1     
=======================================
+ Hits        47142    47155   +13     
  Misses       6248     6248           
+ Partials     1509     1508    -1     

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[math-fehr]

I don't know that much affine parsing, but I trust you otherwise (probably someone that understands this should review this as well)