[DRAFT] Extend GQA fusion for Gemma3

[gramalingam]

Gemma3 applies an extra (simplified) normalization to query and key before the rotary embedding. Extend GQA fusion to handle this.

TODO: will add test-case separately.

[codecov]

Codecov Report

❌ Patch coverage is 22.22222% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.35%. Comparing base (8089bc7) to head (7c5f947).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
onnxscript/rewriter/ort_fusions/gqa.py	22.22%	12 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2639      +/-   ##
==========================================
- Coverage   70.39%   70.35%   -0.04%     
==========================================
  Files         222      222              
  Lines       26294    26312      +18     
  Branches     2630     2632       +2     
==========================================
+ Hits        18509    18513       +4     
- Misses       6865     6877      +12     
- Partials      920      922       +2     

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