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/button.rs

@@ -0,0 +1,91 @@
+use gpui::AnyView;
+
+use crate::prelude::*;
+use crate::{ButtonCommon, ButtonLike, ButtonSize2, ButtonStyle2, Label, LineHeightStyle};
+
+#[derive(IntoElement)]
+pub struct Button {
+    base: ButtonLike,
+    label: SharedString,
+    label_color: Option<Color>,
+    selected: bool,
+}
+
+impl Button {
+    pub fn new(id: impl Into<ElementId>, label: impl Into<SharedString>) -> Self {
+        Self {
+            base: ButtonLike::new(id),
+            label: label.into(),
+            label_color: None,
+            selected: false,
+        }
+    }
+
+    pub fn selected(mut self, selected: bool) -> Self {
+        self.selected = selected;
+        self
+    }
+
+    pub fn color(mut self, label_color: impl Into<Option<Color>>) -> Self {
+        self.label_color = label_color.into();
+        self
+    }
+}
+
+impl Clickable for Button {
+    fn on_click(
+        mut self,
+        handler: impl Fn(&gpui::ClickEvent, &mut WindowContext) + 'static,
+    ) -> Self {
+        self.base = self.base.on_click(handler);
+        self
+    }
+}
+
+impl Disableable for Button {
+    fn disabled(mut self, disabled: bool) -> Self {
+        self.base = self.base.disabled(disabled);
+        self
+    }
+}
+
+impl ButtonCommon for Button {
+    fn id(&self) -> &ElementId {
+        self.base.id()
+    }
+
+    fn style(mut self, style: ButtonStyle2) -> Self {
+        self.base = self.base.style(style);
+        self
+    }
+
+    fn size(mut self, size: ButtonSize2) -> Self {
+        self.base = self.base.size(size);
+        self
+    }
+
+    fn tooltip(mut self, tooltip: impl Fn(&mut WindowContext) -> AnyView + 'static) -> Self {
+        self.base = self.base.tooltip(tooltip);
+        self
+    }
+}
+
+impl RenderOnce for Button {
+    type Rendered = ButtonLike;
+
+    fn render(self, _cx: &mut WindowContext) -> Self::Rendered {
+        let label_color = if self.base.disabled {
+            Color::Disabled
+        } else if self.selected {
+            Color::Selected
+        } else {
+            Color::Default
+        };
+
+        self.base.child(
+            Label::new(self.label)
+                .color(label_color)
+                .line_height_style(LineHeightStyle::UILabel),
+        )
+    }
+}