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/workspace2/src/toolbar.rs

@@ -94,9 +94,9 @@ impl Render for Toolbar {
                             .border()
                             .border_color(gpui::red())
                             .p_1()
-                            .child(Button::new("crates"))
+                            .child(Button::new("breadcrumb_crates", "crates"))
                             .child(Label::new("/").color(Color::Muted))
-                            .child(Button::new("workspace2")),
+                            .child(Button::new("breadcrumb_workspace2", "workspace2")),
                     )
                     // Toolbar right side
                     .child(