Cascade slide ball's opacity and the Slider's
Also cascade the colours
Merge branch 'v3' into patch-12

Conflicts:
	cocos/ui/UISlider.cpp
Fix formatting
Merge pull request #7675 from darkdukey/chore/reuse-file-utils-for-video-path

Chore/reuse file utils for video path
Merge pull request #7674 from darkdukey/patch-12

Fix opacity for Slider