Add keymatch modes so terminal can have cmd-k (#4219)

This isn't my favorite idea of a fix, but it does work for now, and it
seems likely the terminal will need to configure other aspects of action
dispatch in the future.

In the future we should explore making it possible to do this via the
keymap, either by making disabling bindings more robust; or by having a
way to indicate immediate mode per binding.

Release Notes:

- Fixed a bug where cmd-k in terminal took 1s

crates/gpui/src/window.rs

@@ -2,11 +2,12 @@ use crate::{
     px, size, transparent_black, Action, AnyDrag, AnyView, AppContext, Arena, AsyncWindowContext,
     AvailableSpace, Bounds, Context, Corners, CursorStyle, DispatchActionListener, DispatchNodeId,
     DispatchTree, DisplayId, Edges, Effect, Entity, EntityId, EventEmitter, FileDropEvent, Flatten,
-    GlobalElementId, Hsla, KeyBinding, KeyContext, KeyDownEvent, KeyMatch, KeymatchResult,
-    Keystroke, KeystrokeEvent, Model, ModelContext, Modifiers, MouseButton, MouseMoveEvent,
-    MouseUpEvent, Pixels, PlatformAtlas, PlatformDisplay, PlatformInput, PlatformWindow, Point,
-    PromptLevel, Render, ScaledPixels, SharedString, Size, SubscriberSet, Subscription,
-    TaffyLayoutEngine, Task, View, VisualContext, WeakView, WindowBounds, WindowOptions,
+    GlobalElementId, Hsla, KeyBinding, KeyContext, KeyDownEvent, KeyMatch, KeymatchMode,
+    KeymatchResult, Keystroke, KeystrokeEvent, Model, ModelContext, Modifiers, MouseButton,
+    MouseMoveEvent, MouseUpEvent, Pixels, PlatformAtlas, PlatformDisplay, PlatformInput,
+    PlatformWindow, Point, PromptLevel, Render, ScaledPixels, SharedString, Size, SubscriberSet,
+    Subscription, TaffyLayoutEngine, Task, View, VisualContext, WeakView, WindowBounds,
+    WindowOptions,
 };
 use anyhow::{anyhow, Context as _, Result};
 use collections::FxHashSet;
@@ -1214,12 +1215,21 @@ impl<'a> WindowContext<'a> {
             .dispatch_path(node_id);
 
         if let Some(key_down_event) = event.downcast_ref::<KeyDownEvent>() {
-            let KeymatchResult { bindings, pending } = self
+            let KeymatchResult {
+                bindings,
+                mut pending,
+            } = self
                 .window
                 .rendered_frame
                 .dispatch_tree
                 .dispatch_key(&key_down_event.keystroke, &dispatch_path);
 
+            if self.window.rendered_frame.dispatch_tree.keymatch_mode == KeymatchMode::Immediate
+                && !bindings.is_empty()
+            {
+                pending = false;
+            }
+
             if pending {
                 let mut currently_pending = self.window.pending_input.take().unwrap_or_default();
                 if currently_pending.focus.is_some() && currently_pending.focus != self.window.focus