Generic/DisallowYodaConditions: improve code coverage

[rodrigoprimo]

Description

This PR improves code coverage for the Generic.ControlStructures.DisallowYodaConditions sniff. It adds a few tests for uncovered lines and documents using tests a few comparison operators that this sniff listens for that were not part of the tests before.

Besides that, this PR removes an unused variable, fixes a typo in a code comment, removes two unreachable variables, and renames a variable to make it more clear what it contains.

It is impossible to add code coverage for the line below using the current test framework and we should not remove it as external sniffs could be using the DisallowYodaConditionsSniff::isArrayStatic() and relying on the current behavior (returning true if the passed token index is not an array):

https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/30b3148b302aaba28d72bdb2432b144ff9d47751/src/Standards/Generic/Sniffs/ControlStructures/DisallowYodaConditionsSniff.php#L152

I left a comment documenting that the line cannot be covered by tests but cannot be removed as well.

I considered using // @codeCoverageIgnore or // @codeCoverageIgnoreStart and // @codeCoverageIgnoreEnd, but that is not possible as well as those annotations trigger different sniff errors for the coding standard used by PHPCS (Squiz.Commenting.PostStatementComment.Found and Squiz.Commenting.InlineComment.InvalidEndChar). I will open a separate issue for this.

Related issues/external references

Part of https://github.com/PHPCSStandards/PHP_CodeSniffer/issues/146

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
  • [ ] This change is only breaking for integrators, not for external standards or end-users.
• [ ] Documentation improvement

PR checklist

• [x] I have checked there is no other PR open for the same change.
• [x] I have read the Contribution Guidelines.
• [x] I grant the project the right to include and distribute the code under the BSD-3-Clause license (and I have the right to grant these rights).
• [x] I have added tests to cover my changes.
• [x] I have verified that the code complies with the projects coding standards.
• [ ] [Required for new sniffs] I have added XML documentation for the sniff.

[jrfnl]

I've rebased the PR without changes (other than re-organizing the commits, but no changes to the code). Merging once the build has passed.