Navigation: Remove navigation highlights when on subpages/posts

[jasmussen]

From WordPress/wporg-main-2022#221

When in subpages, the top nav highlights the main page. Worth removing to not mislead the user with wayfinding.

As an example, in the main news section, the item is highlighted:

When in subpages or permalinks, it remains highlighted (parent):

This is similar in About and About subpages:

While the ability to highlight the parent and ancestor of a page or post is a pattern we're leveraging here, it hasn't materially aided wayfinding, and has caused a few issues on its own.

Should we hide this highlight? It seems especially an issue on mobile:

[ryelle]

Is there a determined outcome here? It sounds like this is still under discussion to me.

[ryelle]

From the discussion on our call yesterday, the outcome here is to stop highlighting when in the section — the top level item should only be highlighted when it's an exact match for the page.

[ryelle]

The "Forums" (and "Learn") section should not be highlighted when on the search page. See WordPress/wporg-main-2022#216