Fix for button flickering issue when video call screen rotates

Issue:
Buttons flicker when rotating video call screen and full screen mode.
Because initial state of these buttons(components) are "visible".
In full screen mode, these buttons should not be "visible" when video
call screen is rotated.

This patch modifies state of these buttons to "invisible" when video
call screen rotates and isFullscreen()==True to fix the flicker issue.
And, adding "enterFullscreenMode()" for getting correct view-size when
changing layout by videocall-screen regenerated.

Test: manual - Checked that not button flickering issue when video call
screen during full screen mode rotates.
Bug: 111242931

Change-Id: I271ae3fa395fa648a89c8debc5c0a76e1a0a5ecd