gpui: Store action documentation (#33809)

Closes #ISSUE

Adds a new `documentation` method to actions, that is extracted from doc
comments when using the `actions!` or derive macros.

Additionally, this PR adds doc comments to as many action definitions in
Zed as possible.

Release Notes:

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

crates/collab_ui/src/channel_view.rs

@@ -30,7 +30,13 @@ use workspace::{
 };
 use workspace::{item::Dedup, notifications::NotificationId};
 
-actions!(collab, [CopyLink]);
+actions!(
+    collab,
+    [
+        /// Copies a link to the current position in the channel buffer.
+        CopyLink
+    ]
+);
 
 pub fn init(cx: &mut App) {
     workspace::FollowableViewRegistry::register::<ChannelView>(cx)

crates/collab_ui/src/chat_panel.rs

@@ -71,7 +71,13 @@ struct SerializedChatPanel {
     width: Option<Pixels>,
 }
 
-actions!(chat_panel, [ToggleFocus]);
+actions!(
+    chat_panel,
+    [
+        /// Toggles focus on the chat panel.
+        ToggleFocus
+    ]
+);
 
 impl ChatPanel {
     pub fn new(

crates/collab_ui/src/collab_panel.rs

@@ -44,15 +44,25 @@ use workspace::{
 actions!(
     collab_panel,
     [
+        /// Toggles focus on the collaboration panel.
         ToggleFocus,
+        /// Removes the selected channel or contact.
         Remove,
+        /// Opens the context menu for the selected item.
         Secondary,
+        /// Collapses the selected channel in the tree view.
         CollapseSelectedChannel,
+        /// Expands the selected channel in the tree view.
         ExpandSelectedChannel,
+        /// Starts moving a channel to a new location.
         StartMoveChannel,
+        /// Moves the selected item to the current location.
         MoveSelected,
+        /// Inserts a space character in the filter input.
         InsertSpace,
+        /// Moves the selected channel up in the list.
         MoveChannelUp,
+        /// Moves the selected channel down in the list.
         MoveChannelDown,
     ]
 );

crates/collab_ui/src/collab_panel/channel_modal.rs

@@ -17,9 +17,13 @@ use workspace::{ModalView, notifications::DetachAndPromptErr};
 actions!(
     channel_modal,
     [
+        /// Selects the next control in the channel modal.
         SelectNextControl,
+        /// Toggles between invite members and manage members mode.
         ToggleMode,
+        /// Toggles admin status for the selected member.
         ToggleMemberAdmin,
+        /// Removes the selected member from the channel.
         RemoveMember
     ]
 );

crates/collab_ui/src/notification_panel.rs

@@ -74,7 +74,13 @@ pub struct NotificationPresenter {
     pub can_navigate: bool,
 }
 
-actions!(notification_panel, [ToggleFocus]);
+actions!(
+    notification_panel,
+    [
+        /// Toggles focus on the notification panel.
+        ToggleFocus
+    ]
+);
 
 pub fn init(cx: &mut App) {
     cx.observe_new(|workspace: &mut Workspace, _, _| {