keymap_ui: Editor for action input in modal (#34080)

Closes #ISSUE

Adds a very simple editor for editing action input to the edit keybind
modal. No auto-complete yet.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/settings/src/keymap_file.rs

@@ -426,12 +426,18 @@ impl KeymapFile {
         }
     }
 
+    /// Creates a JSON schema generator, suitable for generating json schemas
+    /// for actions
+    pub fn action_schema_generator() -> schemars::SchemaGenerator {
+        schemars::generate::SchemaSettings::draft2019_09().into_generator()
+    }
+
     pub fn generate_json_schema_for_registered_actions(cx: &mut App) -> Value {
         // instead of using DefaultDenyUnknownFields, actions typically use
         // `#[serde(deny_unknown_fields)]` so that these cases are reported as parse failures. This
         // is because the rest of the keymap will still load in these cases, whereas other settings
         // files would not.
-        let mut generator = schemars::generate::SchemaSettings::draft2019_09().into_generator();
+        let mut generator = Self::action_schema_generator();
 
         let action_schemas = cx.action_schemas(&mut generator);
         let deprecations = cx.deprecated_actions_to_preferred_actions();