ref(issue-views): Restructure issue views components (#82593)

This PR reorganizes some of the components and logic in IssueViews
components. **No visual or functional changes should are intended by
these changes.** If you see any in the preview, please lmk.

The biggest changes include: 
* **Delete `draggableTabBar.tsx`** component, redistribute it's parts to
other components (detailed in the diff)
* **Create a new `IssueViewTab` component that contains the tab contents
(title, ellipsis menu, etc.).**
* Rename `draggableTabMenuButton.tsx` to `issueViewEllipsisMenu.tsx`
* Rename `draggableTabs` to `views` in `customViewsHeader.tsx`

Some reasoning: 
* `DraggableTabBar` sounds very redundant to and less clear than
`CustomViewsHeader` and `DraggableTabList`. To me, CustomViewsHeader
(soon to be renamed IssueViewsHeader) should be a specific
implementation of `DraggableTabList`, which sounds like it should be
reusable.
* I'd like to have parity between product names and codebase names -
hence why I'm changing "custom views" to "issue views" and "tabs" to
views.