Implement XCB framebuffer plugin (port from x11)

Previously used x11 plugin does not compile with Qt5, because Qt5 does
not use Xlib, it uses xcb. Rewrite screen capture plugin from Xlib to
xcb.

I made xcb libs compile required dependency, but availability of X
shared memory extension is checked at runtime. It is used to effectively
get image pixels data, instead of transfering 8Mb over the wire. Xdamage
is used to limit image getting operations only within actually changed
rectangles of screen.

BUG: 377998

Tested on single-monitor system and dual-monitor, where primary monitor
does not start at (0,0) coordinate. Image transfer works fine.
Dual-monitor only has problems with receiving mouse cursor position and
clicks, but this should be fixed outside of framebuffer plugin.

Differential Revision: https://phabricator.kde.org/D5211