WindowServer: Don't use GNU-style designator

Clang throws a fit when it encounters this code, since we already have
the standardized designated initializer syntax in C++20, which we should
use.

Userland/Services/WindowServer/Screen.cpp

@@ -419,10 +419,10 @@ void Screen::flush_display_front_buffer(int front_buffer_index, Gfx::IntRect& re
     VERIFY(m_can_device_flush_buffers);
     auto scale_factor = this->scale_factor();
     FBRect flush_rect {
-        x : (unsigned)(rect.x() * scale_factor),
-        y : (unsigned)(rect.y() * scale_factor),
-        width : (unsigned)(rect.width() * scale_factor),
-        height : (unsigned)(rect.height() * scale_factor)
+        .x = (unsigned)(rect.x() * scale_factor),
+        .y = (unsigned)(rect.y() * scale_factor),
+        .width = (unsigned)(rect.width() * scale_factor),
+        .height = (unsigned)(rect.height() * scale_factor)
     };
 
     if (fb_flush_buffers(m_framebuffer_fd, front_buffer_index, &flush_rect, 1) < 0) {