Fix bindings_for_action handling of shadowed key bindings (#32220)

Fixes two things:

* ~3 months ago [in PR
#26420](https://github.com/zed-industries/zed/pull/26420/files#diff-33b58aa2da03d791c2c4761af6012851b7400e348922d64babe5fd48ac2a8e60)
`bindings_for_action` was changed to return bindings even when they are
shadowed (when the keystrokes would actually do something else).

* For edit prediction keybindings there was some odd behavior where
bindings for `edit_prediction_conflict` were taking precedence over
bindings for `edit_prediction` even when the `edit_prediction_conflict`
predicate didn't match. The workaround for this was #24812. The way it
worked was:

    - List all bindings for the action

- For each binding, get the highest precedence binding with the same
input sequence

- If the highest precedence binding has the same action, include this
binding. This was the bug - this meant that if a binding in the keymap
has the same keystrokes and action it can incorrectly take display
precedence even if its context predicate does not pass.

- Fix is to check that the highest precedence binding is a full match.
To do this efficiently, it's based on an index within the keymap
bindings.

Also adds `highest_precedence_binding_*` variants which avoid the
inefficiency of building lists of bindings just to use the last.

Release Notes:

- Fixed display of keybindings to skip bindings that are shadowed by a
binding that uses the same keystrokes.
- Fixed display of `editor::AcceptEditPrediction` bindings to use the
normal precedence that prioritizes user bindings.

crates/editor/src/editor.rs

@@ -2261,24 +2261,13 @@ impl Editor {
             window.bindings_for_action_in_context(&AcceptEditPrediction, key_context)
         };
 
-        AcceptEditPredictionBinding(
-            bindings
-                .into_iter()
-                .filter(|binding| {
-                    !in_conflict
-                        || binding
-                            .keystrokes()
-                            .first()
-                            .map_or(false, |keystroke| keystroke.modifiers.modified())
-                })
-                .rev()
-                .min_by_key(|binding| {
-                    binding
-                        .keystrokes()
-                        .first()
-                        .map_or(u8::MAX, |k| k.modifiers.number_of_modifiers())
-                }),
-        )
+        AcceptEditPredictionBinding(bindings.into_iter().rev().find(|binding| {
+            !in_conflict
+                || binding
+                    .keystrokes()
+                    .first()
+                    .map_or(false, |keystroke| keystroke.modifiers.modified())
+        }))
     }
 
     pub fn new_file(