core: reuse field definition functions across op definitions

[superlopuh]

We can reuse the function instances, so there's no need to redefine them for every operation definition.

Slight perf improvement for make filecheck, but it's annoyingly close to the margin off error, I look forward to seeing the perf results later. I also have a feeling that it should help pypy's tracing to have only one of each of these functions for all of xDSL, instead of one per op.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.18%. Comparing base (c9493b7) to head (37d2ee5).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4016      +/-   ##
==========================================
- Coverage   90.19%   90.18%   -0.01%     
==========================================
  Files         458      458              
  Lines       58288    58314      +26     
  Branches     5687     5688       +1     
==========================================
+ Hits        52570    52593      +23     
- Misses       4328     4331       +3     
  Partials     1390     1390              

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