Allow to use premultiplied external texture

Allow to use premultiplied external texture

FrameBuffer result colortexture is premultiplied always.
So make we always use premultiplied texture.

And make a way to user determine native image source is premultiplied or not.

+

Since FBO texture always premultiplied, revert scene view's trick
https://review.tizen.org/gerrit/c/platform/core/uifw/dali-toolkit/+/285486

Change-Id: I72bfe4a04a69c259d983e9dc74086cefcdd4cc7d
Signed-off-by: Eunki Hong <eunkiki.hong@samsung.com>