Improve navigation between projects within a group/subgroup
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### Problem to solve
It's a real pain to navigate between projects within a group/subgroup
### Further details
Navigating between issues and merge requests within a single project that is comprised of multiple repo's is very slow, I'm hoping it can be sped up.
### Proposal
Breadcrumbs component for project within a group becomes a dropdown for all projects within that group.
Let's take this hierarchy for a project called `MyProject`:
* Level 1
* Group A
* Group B
* Subgroup X
* Subgroup Y
* MyProject
* Subgroup Z
* Group C
If the truncated breadcrumb looks like this:
Level 1 > `...` > MyProject
The previous breadcrumb menu on ellipsis would show:
* Group B
* Subgroup Y
Now with https://gitlab.com/gitlab-org/gitlab/-/issues/338012 when we click on the ellipsis the breadcrumb expands to:
Level 1 > Group B > Subgroup Y > MyProject
Now if each of the segment/section/slice of the breadcrumb is a dropdown...
Clicking on Group B would show:
* Group A
* Group B (selected)
* Group C
Or, clicking on "Subgroup Y" would show:
* Subgroup X
* Subgroup Y (selected)
* Subgroup Z
This is similar to the dropdown navigation that you see in VSCode

### What does success look like, and how can we measure that?
Navigation speed is greatly improved

### Links / references
issue