[Styles Pane]: Allow keyboard navigation on filtered sections list
[Styles Pane]: Allow keyboard navigation on filtered sections list

Issue:
- Filtered section list in styles sidebar is not keyboard navigable

Changes:
- When filtering, a new sections list is not generated, but rather sections that don't match the filter are hidden.
- Added findVisibleSiblingRecursive function which iterates through the list to find the next logical visible section
    - Only called when there is a filter applied to the sections list.

Fixed (GIF): https://imgur.com/Htg9ikY

Bug: 1182469
Change-Id: I1a84abdae6c5e981abe2edfd7f927f951a10b3a0
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2716819
Commit-Queue: Michael Liao <00d75d81082fdf74688ec453c516b42f7cbf0f40@microsoft.com>
Reviewed-by: Alex Rudenko <d8d88e7d7e77f69e23d1d1432231196fb8e02a62@chromium.org>
Reviewed-by: Patrick Brosset <f0b1693d3ec18fb190dd6deddb896f34ba3fd693@microsoft.com>

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