Split Interactive into Interactive and Toggleable (#2628)

This is a part of the intensity driven theme rewrite. 

It introduces the `toggle` and `interactive` helper functions to build
Toggle<T> and Interactive<T> styles for interactive elements in the
theme.

This PR also removes the `theme_testbench` crate and related actions.

Huge thanks to @osiewicz and @mikayla-maki for pushing this forward 🙏🏽

Release Notes:

- Updated the style of many interactive elements.

crates/editor/src/element.rs

@@ -1529,7 +1529,7 @@ impl EditorElement {
 
                         enum JumpIcon {}
                         MouseEventHandler::<JumpIcon, _>::new((*id).into(), cx, |state, _| {
-                            let style = style.jump_icon.style_for(state, false);
+                            let style = style.jump_icon.style_for(state);
                             Svg::new("icons/arrow_up_right_8.svg")
                                 .with_color(style.color)
                                 .constrained()
@@ -2094,7 +2094,7 @@ impl Element<Editor> for EditorElement {
                     .folds
                     .ellipses
                     .background
-                    .style_for(&mut cx.mouse_state::<FoldMarkers>(id as usize), false)
+                    .style_for(&mut cx.mouse_state::<FoldMarkers>(id as usize))
                     .color;
 
                 (id, fold, color)