Support outer scope value reference in script

[gramalingam]

This extends onnxscript scripts to allow references to ir.Values defined outside the function. This allows the use of script functions within the construction of graphs using a GraphBuilder.

[codecov]

Codecov Report

❌ Patch coverage is 75.67568% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.78%. Comparing base (ef2bc22) to head (b5d76a2).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
onnxscript/testing/__init__.py	12.50%	6 Missing and 1 partial ⚠️
onnxscript/_internal/builder.py	83.33%	1 Missing ⚠️
onnxscript/_internal/builder_test.py	93.75%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2831   +/-   ##
=======================================
  Coverage   71.78%   71.78%           
=======================================
  Files         239      239           
  Lines       28989    29018   +29     
  Branches     2859     2864    +5     
=======================================
+ Hits        20809    20831   +22     
- Misses       7209     7214    +5     
- Partials      971      973    +2     

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[justinchuby]

@gramalingam there's some lint errors