Add new Button and IconButton components (#3448)

This PR adds new `Button` and `IconButton` components built on top of
our new button abstractions.

Both of these buttons are built from the common `ButtonLike` base, and
implement the `ButtonCommon` (name TBD) trait in order to provide a
common interface.

There are still some visual tweaks that we'll need to make to the new
buttons, but those should be straightforward to make after we land this.

Release Notes:

- N/A

crates/editor2/src/element.rs

@@ -48,6 +48,7 @@ use std::{
 };
 use sum_tree::Bias;
 use theme::{ActiveTheme, PlayerColor};
+use ui::prelude::*;
 use ui::{h_stack, IconButton, Tooltip};
 use util::ResultExt;
 use workspace::item::Item;