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/debugger_ui/src/session/running/breakpoint_list.rs

@@ -33,7 +33,12 @@ use zed_actions::{ToggleEnableBreakpoint, UnsetBreakpoint};
 
 actions!(
     debugger,
-    [PreviousBreakpointProperty, NextBreakpointProperty]
+    [
+        /// Navigates to the previous breakpoint property in the list.
+        PreviousBreakpointProperty,
+        /// Navigates to the next breakpoint property in the list.
+        NextBreakpointProperty
+    ]
 );
 #[derive(Clone, Copy, PartialEq)]
 pub(crate) enum SelectedBreakpointKind {

crates/debugger_ui/src/session/running/console.rs

@@ -23,7 +23,13 @@ use std::{cell::RefCell, ops::Range, rc::Rc, usize};
 use theme::{Theme, ThemeSettings};
 use ui::{ContextMenu, Divider, PopoverMenu, SplitButton, Tooltip, prelude::*};
 
-actions!(console, [WatchExpression]);
+actions!(
+    console,
+    [
+        /// Adds an expression to the watch list.
+        WatchExpression
+    ]
+);
 
 pub struct Console {
     console: Entity<Editor>,

crates/debugger_ui/src/session/running/variable_list.rs

@@ -18,12 +18,19 @@ use util::debug_panic;
 actions!(
     variable_list,
     [
+        /// Expands the selected variable entry to show its children.
         ExpandSelectedEntry,
+        /// Collapses the selected variable entry to hide its children.
         CollapseSelectedEntry,
+        /// Copies the variable name to the clipboard.
         CopyVariableName,
+        /// Copies the variable value to the clipboard.
         CopyVariableValue,
+        /// Edits the value of the selected variable.
         EditVariable,
+        /// Adds the selected variable to the watch list.
         AddWatch,
+        /// Removes the selected variable from the watch list.
         RemoveWatch,
     ]
 );