Implement the XTWINOPS (CSI t) control sequences that "make sense".

These sequences were implemented:

CSI 14 t - report the text area size in pixels
CSI 16 t - report the cell size in pixels
CSI 18 t - report the text area size in cells
CSI 21 t - report the window title

These sequences were not implemented because they manuipulate the window
state in ways that we do not want.

CSI 1 t
CSI 2 t
CSI 3 ; x ; y t
CSI 4 ; height ; width ; t
CSI 5 t
CSI 6 t
CSI 7 t
CSI 8 ; height ; width ; t
CSI 9 ; 0 t
CSI 9 ; 1 t
CSI 9 ; 2 t
CSI 9 ; 3 t
CSI 10 ; 0 t
CSI 10 ; 1 t
CSI 10 ; 2 t
CSI 24 t

These sequences were not implemented because they do not make sense in
a Wayland context:

CSI 11 t
CSI 13 t
CSI 14 ; 2 t

These sequences were not implemented because they provide information
about the screen that is unnecessary.

CSI 15 t
CSI 19 t

These sequences were not implemeted because Ghostty does not maintain an
icon title for windows.

CSI 20 t
CSI 22 ; 0 t
CSI 22 ; 1 t
CSI 23 ; 0 t
CSI 23 ; 1 t

These sequences were not implemented because of the additional
complexity of maintaining a stack of window titles.

CSI 22 ; 2 t
CSI 23 ; 2 t

src/apprt/embedded.zig

@@ -55,6 +55,9 @@ pub const App = struct {
         /// Called to set the title of the window.
         set_title: *const fn (SurfaceUD, [*]const u8) callconv(.C) void,
 
+        /// Called to get the title of the window.
+        get_title: ?*const fn (SurfaceUD) callconv(.C) ?[*]const u8 = null,
+
         /// Called to set the cursor shape.
         set_mouse_shape: *const fn (SurfaceUD, terminal.MouseShape) callconv(.C) void,
 
@@ -543,6 +546,17 @@ pub const Surface = struct {
         );
     }
 
+    pub fn getTitle(self: *Surface) ?[:0]const u8 {
+        const func = self.app.opts.get_title orelse {
+            log.info("runtime embedder does not support get_title", .{});
+            return null;
+        };
+
+        const result = func(self.userdata);
+        if (result == null) return null;
+        return std.mem.sliceTo(@as([*:0]const u8, @ptrCast(result.?)), 0);
+    }
+
     pub fn setMouseShape(self: *Surface, shape: terminal.MouseShape) !void {
         self.app.opts.set_mouse_shape(
             self.userdata,