[452294] Isolate search of opaque pixel in a specific class

to facilitate future reuses.
This commit also
* adds specific tests on this new class
* fixes a bug in
org.eclipse.sirius.diagram.ui.tools.internal.figure.util.OpaquePixelFinder.searchFirstOpaquePoint(int,
Point, ImageFigureWithAlpha, Rectangle). The initial location for RIGHT
is not the box.width but box.width-1 (same for BOTTOM with height).

Change-Id: I579817dd53b6a490b4cc9daa9dcdd6352b488b93
Signed-off-by: Laurent Redor <laurent.redor@obeo.fr>
4 files changed