This change brings new Scoped labels to Issue board as well.
With the last change, this was missed.

- Compare versions header is full width except in the unified diff mode
with no tree sidebar
  - Bar is always full width, but the content within stays centered when
unified and no tree sidebar
- File header is the same height as the "Compare versions header"
- aligns with the design system grid guidelines => 56px
- Diff file headers use a button group, switch icon order to open file
externally being the last option, all buttons will become icon buttons
(icon delivery by @dimitrieh)
- If a file header becomes sticky no rounded corner/double border
problem is visible anymore

This commit adds a resuable UI component that allows a user to search
for a project name, shows the search results, and allows the user to
select one or more projects.  This component communicates with its
parent using props and events.

This component was originally created for use in the EE-specific
"Operations Dashboard" page, but it is applicable for CE use cases as
well, and so was added as a CE shared component.

In addition, some logic was extracted from the frequent_items_list_item
component into shared filters to avoid logic duplication.

- Add an ID to the diff content
- handle clicking on file name in diffFileHeader when it is not a link
to another page but rather a link to an element on the page

Remove duplicate XHR request when requesting new pipeline page

Closes #58095

See merge request gitlab-org/gitlab-ce!25506

When a user clicked on another page in the pipeline page, the following
would happen:

1. PipelinesService.getPipelines() would be called to fetch the new page
2. In the success handler, Poll.restart() would be called
3. This would invoke Poll.makeRequest(), which would fire off a new
request.

To fix this, we introduce a enable(), which will:

1. Update the request data accordingly
2. Clear the old timeout if necessary and start a new timer

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/58095