AIRO-1782 Fix behavior of 'Use URDF Values' check-box (and re-name)

Proposed change(s)

CDP user Robyn described an issue where the "Use URDF Values" check-box didn't behave the way they expected (values are greyed out when box is not checked, and are only "editable" when being "used," although the values were being reset immediately when changed).

Re-named the checkbox to "Override URDF Values" to be more in-line with the toggle-group behavior, and corrected behavior so that when the values are editable, the edits made are appropriately propagated to the underlying ArticulationBody. Also added a button that resets the override values back to those originally defined in the URDF, and added logic so that when the Overrides box is unchecked, it appropriately toggles back to the original URDF values. Also also added a type alias at the top of the file and cleaned up superfluous if #UNITY_EDITOR pre-processor directives.

Tested manually in editor.

Useful links (GitHub issues, JIRA tickets, forum threads, etc.)

Provide any relevant links here.

Types of change(s)

[x] Bug fix
[x] Code refactor

Checklist

[x] Ensured this PR is up-to-date with the dev branch
[x] Created this PR to target the dev branch
[x] Followed the style guidelines as described in the Contribution Guidelines
[x] Updated the Changelog and described changes in the Unreleased section

https://user-images.githubusercontent.com/29758400/162850424-e9de5550-4e63-4cf7-a0f4-ad56128c4bb9.mp4

Unity-Technologies / URDF-Importer