Separate out operator vs model testing. (#16228)
### Description
<!-- Describe your changes. -->
Split up OpTester to separate out operator vs model testing. This led to
a lot of other cleanups/refactoring.
- create BaseTester class and derived OpTester/ModelTester classes to
limit APIs to what is applicable for each test type
- e.g. adding an attribute isn't relevant to a model test
- cleanup structure
- don't expose member variables either directly or via public methods
returning them
- split out checkers so they can be easily re-used
- refactor so there's one public Check method for comparing two OrtValue
instances containing any data type
- refactor the GradientOpTester usage
- it required a lot of OpTester internals to be exposed and no other
tests needed this
- it also returned Status through various parts which prevented the
usage of the google test macros which provide better output. change to
return void and use the macros.
- fix some other minor issues
- update some cmake files so all the source files are included
- remove some low value helpers (FetchTensor and GetShapeVector)
- remove some outdated code to allow unreleased opset versions from when
onnx opset 15 wasn't released
- move files from test/util/include/test to test/util/include
- doesn't seem to be any reason for the additional subdirectory given
they're not files use to test the code in test/util
- files were moved with no changes
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
Cleanup test infrastructure.
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Co-authored-by: Edward Chen <18449977+edgchen1@users.noreply.github.com>
