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/key_dispatch.rs

@@ -62,6 +62,16 @@ use std::{
     rc::Rc,
 };
 
+/// KeymatchMode controls how keybindings are resolved in the case of conflicting pending keystrokes.
+/// When `Sequenced`, gpui will wait for 1s for sequences to complete.
+/// When `Immediate`, gpui will immediately resolve the keybinding.
+#[derive(Default, PartialEq)]
+pub enum KeymatchMode {
+    #[default]
+    Sequenced,
+    Immediate,
+}
+
 #[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
 pub(crate) struct DispatchNodeId(usize);
 
@@ -74,6 +84,7 @@ pub(crate) struct DispatchTree {
     keystroke_matchers: FxHashMap<SmallVec<[KeyContext; 4]>, KeystrokeMatcher>,
     keymap: Rc<RefCell<Keymap>>,
     action_registry: Rc<ActionRegistry>,
+    pub(crate) keymatch_mode: KeymatchMode,
 }
 
 #[derive(Default)]
@@ -105,6 +116,7 @@ impl DispatchTree {
             keystroke_matchers: FxHashMap::default(),
             keymap,
             action_registry,
+            keymatch_mode: KeymatchMode::Sequenced,
         }
     }
 
@@ -115,6 +127,7 @@ impl DispatchTree {
         self.focusable_node_ids.clear();
         self.view_node_ids.clear();
         self.keystroke_matchers.clear();
+        self.keymatch_mode = KeymatchMode::Sequenced;
     }
 
     pub fn push_node(