settings_ui: Add pickers for theme and icon themes (#40829)

In the process of adding pickers for the theme and icon themes fields in
the settings UI, I felt like there was an improvement opportunity in
regards to where some of these components are stored. The `ui_input`
crate originally was meant only for the text field-like component, which
couldn't be in the regular `ui` crate due to the dependency with
`editor`. Given we had also added the number field there—which is
similar in also having the same dependency—it made sense to think of
this crate more like a home for form-like components rather than for
only one component.

However, we were also storing some settings UI-specific stuff in that
crate, which didn't feel right. So I ended up creating a new directory
within the `settings_ui` for components and moved all the pickers and
the custom input field there. I think this makes it for a cleaner
structure.

Release Notes:

- settings_ui: Added the ability to search for theme and icon themes in
their respective fields.

crates/zeta2_tools/src/zeta2_tools.rs

@@ -17,7 +17,7 @@ use language::{Buffer, DiskState};
 use ordered_float::OrderedFloat;
 use project::{Project, WorktreeId, telemetry_snapshot::TelemetrySnapshot};
 use ui::{ButtonLike, ContextMenu, ContextMenuEntry, DropdownMenu, KeyBinding, prelude::*};
-use ui_input::SingleLineInput;
+use ui_input::InputField;
 use util::{ResultExt, paths::PathStyle, rel_path::RelPath};
 use workspace::{Item, SplitDirection, Workspace};
 use zeta2::{PredictionDebugInfo, Zeta, Zeta2FeatureFlag, ZetaOptions};
@@ -65,11 +65,11 @@ pub struct Zeta2Inspector {
     focus_handle: FocusHandle,
     project: Entity<Project>,
     last_prediction: Option<LastPrediction>,
-    max_excerpt_bytes_input: Entity<SingleLineInput>,
-    min_excerpt_bytes_input: Entity<SingleLineInput>,
-    cursor_context_ratio_input: Entity<SingleLineInput>,
-    max_prompt_bytes_input: Entity<SingleLineInput>,
-    max_retrieved_declarations: Entity<SingleLineInput>,
+    max_excerpt_bytes_input: Entity<InputField>,
+    min_excerpt_bytes_input: Entity<InputField>,
+    cursor_context_ratio_input: Entity<InputField>,
+    max_prompt_bytes_input: Entity<InputField>,
+    max_retrieved_declarations: Entity<InputField>,
     active_view: ActiveView,
     zeta: Entity<Zeta>,
     _active_editor_subscription: Option<Subscription>,
@@ -225,9 +225,9 @@ impl Zeta2Inspector {
         label: &'static str,
         window: &mut Window,
         cx: &mut Context<Self>,
-    ) -> Entity<SingleLineInput> {
+    ) -> Entity<InputField> {
         let input = cx.new(|cx| {
-            SingleLineInput::new(window, cx, "")
+            InputField::new(window, cx, "")
                 .label(label)
                 .label_min_width(px(64.))
         });
@@ -241,7 +241,7 @@ impl Zeta2Inspector {
                 };
 
                 fn number_input_value<T: FromStr + Default>(
-                    input: &Entity<SingleLineInput>,
+                    input: &Entity<InputField>,
                     cx: &App,
                 ) -> T {
                     input