Introduce reset_window_size keybinding and apprt action

Related to #6035

This implements the keybind/action portion of #5974 so that this can
have a binding and so that other apprts can respond to this and
implement it this way.

src/Surface.zig

@@ -4228,6 +4228,12 @@ pub fn performBindingAction(self: *Surface, action: input.Binding.Action) !bool
             {},
         ),
 
+        .reset_window_size => return try self.rt_app.performAction(
+            .{ .surface = self },
+            .reset_window_size,
+            {},
+        ),
+
         .toggle_maximize => return try self.rt_app.performAction(
             .{ .surface = self },
             .toggle_maximize,

src/apprt/action.zig

@@ -140,6 +140,10 @@ pub const Action = union(Key) {
     /// Sets a size limit (in pixels) for the target terminal.
     size_limit: SizeLimit,
 
+    /// Resets the window size to the default size. See the
+    /// `reset_window_size` keybinding for more information.
+    reset_window_size,
+
     /// Specifies the initial size of the target terminal.
     ///
     /// This may be sent once during the initialization of a surface
@@ -259,6 +263,7 @@ pub const Action = union(Key) {
         toggle_split_zoom,
         present_terminal,
         size_limit,
+        reset_window_size,
         initial_size,
         cell_size,
         inspector,

src/apprt/glfw.zig

@@ -240,6 +240,7 @@ pub const App = struct {
             .config_change,
             .toggle_maximize,
             .prompt_title,
+            .reset_window_size,
             => {
                 log.info("unimplemented action={}", .{action});
                 return false;

src/apprt/gtk/App.zig

@@ -512,6 +512,7 @@ pub fn performAction(
         .render_inspector,
         .renderer_health,
         .color_change,
+        .reset_window_size,
         => {
             log.warn("unimplemented action={}", .{action});
             return false;

src/input/Binding.zig

@@ -380,6 +380,11 @@ pub const Action = union(enum) {
     /// Equalize all splits in the current window
     equalize_splits: void,
 
+    /// Reset the window to the default size. The "default size" is the
+    /// size that a new window would be created with. This has no effect
+    /// if the window is fullscreen.
+    reset_window_size: void,
+
     /// Control the terminal inspector visibility.
     ///
     /// Arguments:
@@ -772,6 +777,7 @@ pub const Action = union(enum) {
             .toggle_fullscreen,
             .toggle_window_decorations,
             .toggle_secure_input,
+            .reset_window_size,
             .crash,
             => .surface,