Allow rewriter input/output to be IR

[gramalingam]

Allow rewriter input/output to be IR.

Eventually, we will keep all intermediate form in IR (switching to proto only at end).

Issue #1401

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 76.51%. Comparing base (523e466) to head (91355b4).

Files	Patch %	Lines
onnxscript/rewriter/__init__.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1639   +/-   ##
=======================================
  Coverage   76.50%   76.51%           
=======================================
  Files         234      234           
  Lines       24743    24743           
  Branches     4364     4364           
=======================================
+ Hits        18929    18931    +2     
+ Misses       4971     4969    -2     
  Partials      843      843           

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[github-actions]

Test Results

     30 files  ±     0       30 suites  ±0   3h 20m 54s ⏱️ +51s
 10 516 tests + 2 185    8 635 ✅ +1 766    1 879 💤 +   419  2 ❌ +2 
576 204 runs   - 17 906  119 675 ✅  - 2 643  456 527 💤  - 15 263  2 ❌ +2 

For more details on these failures, see this check.

Results for commit 91355b4. ± Comparison against base commit 523e466.