fix(tests): Make test imports correct and more consistent

[cpcallen]

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide
• I ran npm run format and npm run lint

The details

Resolves

Addresses the cause of #7224 being filed, though without making more than a token effort to address the issue as written.

Proposed Changes

• Fix invalid import paths in mocha tests. This resolves the warnings generated during buildDeps by
  closure-make-deps.

• Fix failing context menu item test:

  • The test appears to have been wrong: Block.prototype.getIcon is typed as
    getIcon(/* ... */): T | undefined
    and documented as "@returns The icon with the given type if it exists on the block, undefined otherwise."

• Clean up inconsistent usage of CommentIcon in the test files touched by PR fix: Utilize getIcon instead of getCommentIcon in tests #7200 to be consistent with existing usage of Blockly.icons.CommentIcon instead of importing it separately.

Behaviour Before Change

• Scary (but apparently not sufficiently scary) warnings generated by closure-make-deps during buildDeps.
• Only 2800 mocha tests were being run, due to errors loading certain test files that were only being reported in the browser console (and one of the non-runners would have failed).

Behaviour After Change

• No deps warnings.
• 2976 mocha tests are run and none fail.

Reason for Changes

Better to run tests than not; better to pass than fail.

Test Coverage

Restored.

Additional Information

Still can't be sure that all mocha tests are actually being run!