keymap_ui: Add auto-complete for context in keybind editor (#34031)

Closes #ISSUE

Implements a very basic completion provider that is attached to the
context editor in the keybind editing modal.

The context identifiers used for completions are scraped from the
default, vim, and base keymaps on demand.

Release Notes:

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

crates/settings/src/settings.rs

@@ -1,3 +1,4 @@
+mod base_keymap_setting;
 mod editable_setting_control;
 mod key_equivalents;
 mod keymap_file;
@@ -11,6 +12,7 @@ use rust_embed::RustEmbed;
 use std::{borrow::Cow, fmt, str};
 use util::asset_str;
 
+pub use base_keymap_setting::*;
 pub use editable_setting_control::*;
 pub use key_equivalents::*;
 pub use keymap_file::{
@@ -71,6 +73,7 @@ pub fn init(cx: &mut App) {
         .set_default_settings(&default_settings(), cx)
         .unwrap();
     cx.set_global(settings);
+    BaseKeymap::register(cx);
 }
 
 pub fn default_settings() -> Cow<'static, str> {