keymap_ui: Add ability to edit context (#34019)

Closes #ISSUE

Adds a context input to the keybind edit modal. Also fixes some bugs in
the keymap update function to handle context changes gracefully. The
current keybind update strategy implemented in this PR is
* when the context doesn't change, just update the binding in place
* when the context changes, but the binding is the only binding in the
keymap section, update the binding _and_ context in place
* when the context changes, and the binding is _not_ the only binding in
the keymap section, remove the existing binding and create a new section
with the update context and binding so as to avoid impacting other
bindings

Release Notes:

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

crates/gpui/src/platform/keystroke.rs

@@ -55,7 +55,7 @@ impl Keystroke {
     ///
     /// This method assumes that `self` was typed and `target' is in the keymap, and checks
     /// both possibilities for self against the target.
-    pub(crate) fn should_match(&self, target: &Keystroke) -> bool {
+    pub fn should_match(&self, target: &Keystroke) -> bool {
         #[cfg(not(target_os = "windows"))]
         if let Some(key_char) = self
             .key_char