view: draw borders around actual dimensions

Previously if the view did not take the size requested, we would draw
the borders around the size we asked the view to take rather than its
actual size.

river/XwaylandView.zig

@@ -114,6 +114,15 @@ pub fn getTitle(self: Self) [*:0]const u8 {
     return self.wlr_xwayland_surface.title;
 }
 
+pub fn getActualBox(self: Self) Box {
+    return .{
+        .x = self.wlr_xwayland_surface.x,
+        .y = self.wlr_xwayland_surface.y,
+        .width = self.wlr_xwayland_surface.width,
+        .height = self.wlr_xwayland_surface.height,
+    };
+}
+
 /// Called when the xwayland surface is destroyed
 fn handleDestroy(listener: ?*c.wl_listener, data: ?*c_void) callconv(.C) void {
     const self = @fieldParentPtr(Self, "listen_destroy", listener.?);