Port the picker and uniform list (#3248)

This adds a `UniformList` element and partially implements `Picker` as a
component, using `UniformList`. Because editor2 isn't fully implemented
yet, the picker doesn't have filtering logic yet. We want to merge this
for now though, to make the UniformList element available for other
crates.

Release Notes:

- N/A

crates/ui2/src/components/checkbox.rs

@@ -128,7 +128,7 @@ impl<V: 'static> Checkbox<V> {
             // click area for the checkbox.
             .size_5()
             // Because we've enlarged the click area, we need to create a
-            // `group` to pass down interaction events to the checkbox.
+            // `group` to pass down interactivity events to the checkbox.
             .group(group_id.clone())
             .child(
                 div()
@@ -148,7 +148,7 @@ impl<V: 'static> Checkbox<V> {
                     .bg(bg_color)
                     .border()
                     .border_color(border_color)
-                    // We only want the interaction states to fire when we
+                    // We only want the interactivity states to fire when we
                     // are in a checkbox that isn't disabled.
                     .when(!self.disabled, |this| {
                         // Here instead of `hover()` we use `group_hover()`