weston-init: add repaint-window=10 to [core] config

weston-init: add repaint-window=10 to [core] config

Weston's default repaint-window is 7ms. At 60 fps the vsync interval is
~16ms. Under load (multi-surface composition or 4K fullscreen
weston-simple-egl), the compositor cannot complete repaints within this
window, causing up to 50% FPS drops.

Changing repaint-window to 10ms gives the compositor sufficient time to
complete repaints before vblank while retaining a 6ms buffer acquisition
window, improving frame delivery consistency without introducing additional
frame latency.

Signed-off-by: Yash Gupta <ygupt@qti.qualcomm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>