fix(engine): aria_hidden_nontabbable / isTabbable not accounting for inert

[tombrunet]

• Rule bug: aria_hidden_nontabbable
• Other (Provide information)
  Also addresses other areas where isTabbable is used

This PR is related to the following issue(s):

• Fixes [BUG] Engine not recognizing "inert" for making items non-focusable #2450

Testing reference:

• Test case added

I have conducted the following for this PR:

• I validated this code in Chrome and FF
• I validated this fix in my local env
• I provided details for testing
• This PR has been reviewed and is ready for test
• I understand that the title of this PR will be used for the next release notes.

Assets to aide review attached

• Links to design artifacts
• Links to video walkthrough of user experience
• Other

Definition of Done

• Peer review complete
• Secondary review complete
• Staging deployment verified