Fix Enzyme pass check and add replace_ir_from_file helper

[tzunghanjuang]

Context:

In the compiler driver, we only check if there is any GradientOpInterface for enzyme. However, it only works for early mlir levels with replace_ir. This PR moves the check to the llvm level and detects any __enzyme_* functions.

The PR also adds an extra helper replace_ir_from_file to read the replacement ir from file.

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.93%. Comparing base (5f3d1d3) to head (6dc72e6).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1204   +/-   ##
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  Coverage   97.93%   97.93%           
=======================================
  Files          77       77           
  Lines       10921    10926    +5     
  Branches      971      971           
=======================================
+ Hits        10695    10700    +5     
  Misses        179      179           
  Partials       47       47           

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