Extract Tab component (#3539)

This PR extracts a new `Tab` component from the tabs implementation in
the workspace.

This will allow us to reuse this component anywhere that we need to use
tabs.

Like our other newer components, the `Tab` component has a relatively
open API.

It accepts `children` (or `child`) as well as a `start_slot` and
`end_slot` to position content in the slots on either end of the
content. These slots also respect the `TabCloseSide` and will switch
positions based on this value.

<img width="763" alt="Screenshot 2023-12-07 at 12 19 42 PM"
src="https://github.com/zed-industries/zed/assets/1486634/78e4db6a-f807-431e-8777-f52f2631e6ed">

Release Notes:

- N/A

crates/ui2/src/components.rs

@@ -13,6 +13,7 @@ mod popover;
 mod popover_menu;
 mod right_click_menu;
 mod stack;
+mod tab;
 mod tooltip;
 
 #[cfg(feature = "stories")]
@@ -33,6 +34,7 @@ pub use popover::*;
 pub use popover_menu::*;
 pub use right_click_menu::*;
 pub use stack::*;
+pub use tab::*;
 pub use tooltip::*;
 
 #[cfg(feature = "stories")]