PR View: Popover Dropdown component

[tidy-dev]

Based on #15326

Description

This PR separates out the popover dropdown logic of the branch select component into a new component that I can reuse for the commit list popover.

I also updated the styles to match the figma better.. however, based on our accessibility meeting recently, I figured the link look would be recommended to be underlined to get the required contrast to be accessible, so I added that. But, now that I see it, I think that the design of this component should be revisited. Maybe since this is a button, it should look like a button. It looks like a button on dotcom (when editable) and we do have a dropdown button to context menu elsewhere in our app (repository add button). But, that I will leave to another PR, this PR is to add the dropdown to popover functionality so I can add the commit selection dropdown.

cc: @gavinmn

Screenshots

Screen.Recording.2022-09-22.at.11.49.55.AM.mov

Release notes

Notes: no-notes

[gavinmn]

Looking good.

But, now that I see it, I think that the design of this component should be revisited. Maybe since this is a button, it should look like a button. It looks like a button on dotcom (when editable) and we do have a dropdown button to context menu elsewhere in our app (repository add button).

I agree that we should change this and we can introduce it in a separate PR.

[sergiou87]

Looks great! 🤩