dialects: (llvm) Implement custom format for llvm.return

[sueszli]

Subset of: #5588

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.16%. Comparing base (af616a9) to head (47088c4).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5602   +/-   ##
=======================================
  Coverage   86.15%   86.16%           
=======================================
  Files         393      393           
  Lines       56308    56309    +1     
  Branches     6492     6492           
=======================================
+ Hits        48513    48516    +3     
+ Misses       6262     6261    -1     
+ Partials     1533     1532    -1     

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[superlopuh]

Insta-approve, thank you!

[sueszli]

Yay :) Thank you so much!