Resolve "common_utils_spec.js fails locally for roundOffFloat"

Closes #61910

See merge request gitlab-org/gitlab-ce!28963

- Added isSafeURL utility based on prior work in gitlab-ee
- Also added isAbsoluteOrRootRelative() and getBaseURL() utils,
  needed by isSafeURL
- Removed URL() fallback because URL() is now polyfilled
- Updated specs

Update tests to use toBeCloseTo instead of toBe for
floating point checks.

More info here:
https://jestjs.io/docs/en/expect#tobeclosetonumber-numdigits

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