Fix Op (Slice complex) | improve dim expression

[titaiwangms]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 72.25%. Comparing base (68d4b9f) to head (361af04).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
onnxscript/function_libs/torch_lib/ops/core.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2094   +/-   ##
=======================================
  Coverage   72.25%   72.25%           
=======================================
  Files         217      217           
  Lines       29143    29143           
  Branches     3463     3463           
=======================================
  Hits        21058    21058           
  Misses       6954     6954           
  Partials     1131     1131           

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