Add X11 backend support for debugging

[HidenoriMatsubayashi]

Supports X11 backend for debugging purposes only when developing Flutter apps. Supporting x11 is the lowest priority task because we don't plan to use x11 in embedded at least now.

• Base implementation with Xlib
• Support window resize
• Support mouse/button input
• Support keyboard input
• Support clipboard
• Support mouse cursor
• Full screen option

[HidenoriMatsubayashi]

Support window resize

Surface does not update properly when resizing xcb window. I should change from xcb to xlib..?