dialects: (cf) Custom Parsing and assert change

[alexarice]

Adds custom parsing to control flow operations. I also changed the message of a cf.assert op to be an attribute instead of a property to agree with mlir, but can revert this if there was a good reason for it (/or split it into a separate pr).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.97%. Comparing base (9c49c49) to head (4f0924f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3132   +/-   ##
=======================================
  Coverage   89.97%   89.97%           
=======================================
  Files         426      426           
  Lines       53712    53715    +3     
  Branches     8320     8320           
=======================================
+ Hits        48326    48330    +4     
  Misses       4043     4043           
+ Partials     1343     1342    -1     

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