core: rename MLIR-specific lexing constructs

[superlopuh]

A cleanup PR renaming some things, I did it in two steps to make the diff smaller on the previous PR.

Note stacked PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.38%. Comparing base (de40dd5) to head (016611c).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3592      +/-   ##
==========================================
- Coverage   90.39%   90.38%   -0.01%     
==========================================
  Files         470      470              
  Lines       59123    59123              
  Branches     5616     5616              
==========================================
- Hits        53443    53441       -2     
- Misses       4233     4234       +1     
- Partials     1447     1448       +1     

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