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/ui2/src/components/button/mod.rs

@@ -0,0 +1,7 @@
+mod button;
+mod button_like;
+mod icon_button;
+
+pub use button::*;
+pub use button_like::*;
+pub use icon_button::*;