Move version_utils to _internal | chore

[justinchuby]

Stack from ghstack (oldest at bottom):

• Auto generate OpSchema for functions | feat(op_schema) #626
• Merge attrs and attr_protos in IRFunction | chore(irbuilder) #625
• -> Move version_utils to _internal | chore #624

Move version_utils to _internal so that it can be used my onnxscript

[codecov]

Codecov Report

Merging #624 (c6505cf) into main (e990f23) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #624   +/-   ##
=======================================
  Coverage   74.28%   74.28%           
=======================================
  Files         107      107           
  Lines       11330    11333    +3     
  Branches     1179     1179           
=======================================
+ Hits         8416     8419    +3     
  Misses       2591     2591           
  Partials      323      323           

Impacted Files	Coverage Δ
onnxscript/_internal/version_utils.py	100.00% <ø> (ø)
...pt/function_libs/torch_aten/graph_building_test.py	89.09% <100.00%> (ø)
...s/function_libs/torch_aten/ops_correctness_test.py	88.81% <100.00%> (ø)
onnxscript/tests/functions/onnxfns1A_test.py	85.45% <100.00%> (+0.26%)	⬆️
onnxscript/tests/functions/onnxfns2_test.py	94.73% <100.00%> (+0.14%)	⬆️
onnxscript/tests/functions/onnxfns_test.py	93.47% <100.00%> (+0.14%)	⬆️

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