refactor(NodeNavigation): Convert to standalone

[hirokiterashima]

Changes

• Convert NodeNavigationComponent to standalone component. This component is used to show/hide the prev/next buttons at the bottom of the page for a tabbed navigation themed unit.
• Clean up code

Test Prep

Make a unit use the tabbed navigation theme. In AT > Project JSON view, add this as the top JSON attribute:

    "theme": "tab",

Test

• In VLE for a unit tab theme (see "Test Prep" above)
  • the prev button is hidden when there is no previous step (e.g., you're on the first step in the unit)
  • the next button is hidden when there is no next step (e.g., you're on the last step in the unit)
  • the prev and next buttons should be visible in other cases

[breity]

LGTM. See inline feedback about comments in the test file.

[geoffreykwan]

🎉 This issue has been resolved in version 5.156.1 🎉

The release is available on GitHub release

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