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/debugger_ui.rs

@@ -32,36 +32,67 @@ pub mod tests;
 actions!(
     debugger,
     [
+        /// Starts a new debugging session.
         Start,
+        /// Continues execution until the next breakpoint.
         Continue,
+        /// Detaches the debugger from the running process.
         Detach,
+        /// Pauses the currently running program.
         Pause,
+        /// Restarts the current debugging session.
         Restart,
+        /// Reruns the current debugging session with the same configuration.
         RerunSession,
+        /// Steps into the next function call.
         StepInto,
+        /// Steps over the current line.
         StepOver,
+        /// Steps out of the current function.
         StepOut,
+        /// Steps back to the previous statement.
         StepBack,
+        /// Stops the debugging session.
         Stop,
+        /// Toggles whether to ignore all breakpoints.
         ToggleIgnoreBreakpoints,
+        /// Clears all breakpoints in the project.
         ClearAllBreakpoints,
+        /// Focuses on the debugger console panel.
         FocusConsole,
+        /// Focuses on the variables panel.
         FocusVariables,
+        /// Focuses on the breakpoint list panel.
         FocusBreakpointList,
+        /// Focuses on the call stack frames panel.
         FocusFrames,
+        /// Focuses on the loaded modules panel.
         FocusModules,
+        /// Focuses on the loaded sources panel.
         FocusLoadedSources,
+        /// Focuses on the terminal panel.
         FocusTerminal,
+        /// Shows the stack trace for the current thread.
         ShowStackTrace,
+        /// Toggles the thread picker dropdown.
         ToggleThreadPicker,
+        /// Toggles the session picker dropdown.
         ToggleSessionPicker,
+        /// Reruns the last debugging session.
         #[action(deprecated_aliases = ["debugger::RerunLastSession"])]
         Rerun,
+        /// Toggles expansion of the selected item in the debugger UI.
         ToggleExpandItem,
     ]
 );
 
-actions!(dev, [CopyDebugAdapterArguments]);
+actions!(
+    dev,
+    [
+        /// Copies debug adapter launch arguments to clipboard.
+        CopyDebugAdapterArguments
+    ]
+);
 
 pub fn init(cx: &mut App) {
     DebuggerSettings::register(cx);