Button2 – Part1 (#3420)

## TODO

- [x] Remove `InteractionState`
- [ ] `Selectable` should use `Selection` instead of a boolean
- [x] Clean out ui2 prelude
- [ ] Build out button2 button types
- [ ] Port old buttons

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <1486634+maxdeviant@users.noreply.github.com>

crates/ui2/src/selectable.rs

@@ -0,0 +1,26 @@
+use gpui::{AnyView, WindowContext};
+
+pub trait Selectable {
+    fn selected(self, selected: bool) -> Self;
+    fn selected_tooltip(
+        self,
+        tooltip: Box<dyn Fn(&mut WindowContext) -> AnyView + 'static>,
+    ) -> Self;
+}
+
+#[derive(Debug, Default, PartialEq, Eq, Hash, Clone, Copy)]
+pub enum Selection {
+    #[default]
+    Unselected,
+    Indeterminate,
+    Selected,
+}
+
+impl Selection {
+    pub fn inverse(&self) -> Self {
+        match self {
+            Self::Unselected | Self::Indeterminate => Self::Selected,
+            Self::Selected => Self::Unselected,
+        }
+    }
+}