Improve the MR item details on the open MRs dropdown in Blob view

Context

Please see: #448868 (closed)

Design

🎨 Figma | Design Discussion

State	Screen
Default
On hover of badge	Use hover state for Actionable badge
On click of badge	Disclosure opens Use active state for Actionable badge The entire line item will link to the relevant MR MR title text is truncated after 2 lines of text UX recommendation is to have a fixed width for the MR title, and variable width to accommodate the width of the largest group of avatars for the MR Assignees

Additional notes

• Max height of the component is <TBD>. Overflow will scroll. This is a small edge case, as expected number of MRs per file is 1 - 2.

Implementation

Implementation breakdown

Context	Deliverable
#448868 (closed)	By the end of Milestone 17.10 we will address (context): A badge to show the correct count of total number of open MRs associated with the file On hover, a popover with a list of MR titles
#520125 (closed) (this)	This issue covers: Expand the dropdown to feature the extra MR information, per the mockup. This is almost complete in !183927 (merged) but a few adjustments are needed: Add showing review author, when there are no assignees. See design feedback !183927 (comment 2389805322) Match mobile to design (see #448868 (comment 2384158623)) Make list item clickable (should open MR) !183927 (comment 2392973719) Add to the UI a way to notify users of the query restriction (only MRs open in the last 30 days targeting this branch will be shown) Add analytics instrumentation Add documentation Add feature tests

Accessibility guidelines for implementation

From #520125 (comment 2421875700):

• GlBadge with tooltip: BTooltip has a known issue, so the element with a tooltip needs both a title and an aria-label attributes
• GlDisclosure component: use :toggle-text="__('A list of open merge requests')" (EDIT: I've changed that a bit because Open merge requests might suggest opening a page with merge requests listing) and text-sr-only props on the dropdown to provide context for screen readers. We can omit the number of the MRs in the toggle text. When going through the disclosure, a screen reader will announce the total number in the disclosure group and then "1 out of 4", "2 out of 4" for each item in the disclosure
• GlDisclosureItem component: we can omit an aria-label for the branch icon in each disclosure item, as it's only decorative.