convert bare assert statements in TestCase methods to self.assertEqual

[pmolodo]

NOTE for reviewing:

Since these changes were automatically generated, I recommend reviewing the libCST script used to generate them, linked below, and a sampling of the changes.

Description of Change(s)

...where appropriate, and the comparison is simple.

This makes errors report more useful information - particularly helpful for infrequent or hard-to-reproduce failures.

These changes were automatically generated using a libCST script to parse source code and make changes in a syntax-safe way. This is the exact script used to make these changes:

https://github.com/pmolodo/convert_assert_statements/blob/f2a096191eef3d61fd7e808feeab6b5111a57042/convert_TestCase_assert_statements_to_assert_methods.py

Link to proposal (if applicable)

Fixes Issue(s)

Checklist

• I have created this PR based on the dev branch

• I have followed the coding conventions

• I have added unit tests that exercise this functionality (Reference:
  testing guidelines)

• I have verified that all unit tests pass with the proposed changes*

• I have submitted a signed Contributor License Agreement (Reference:
  Contributor License Agreement instructions)

*Technically, all unit tests did not pass - but the same set failed that also failed on an unmodified pixar/dev branch. These were the failures (all Usdview / UsdImagingGL):

99% tests passed, 14 tests failed out of 1619

Total Test time (real) = 127.82 sec

The following tests FAILED:
	1508 - testUsdImagingGLTextureResync (Failed)
	1529 - testUsdImagingGLMaterialXLocalCustomNodes_simpleNodes (Failed)
	1598 - testUsdviewLights_yup (Failed)
	1599 - testUsdviewSceneLights (Failed)
	1600 - testUsdviewSceneLights_Delegate (Failed)
	1601 - testUsdviewSceneMaterials (Failed)
	1603 - testUsdviewLightVisibility_varying (Failed)
	1612 - testUsdviewMaterialEdits (Failed)
	1615 - testUsdviewCPUSkinning (Failed)
	1616 - testUsdviewGPUSkinning (Failed)
	1618 - testUsdviewPrimvarEdits (Failed)
	1619 - testUsdviewOIT (Failed)
	1620 - testUsdviewAdditive (Failed)
	1623 - testUsdviewPointInstancerVariant (Failed)

[jesschimein]

Filed as internal issue #USD-11845

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