[424422] Fix test APIs which relied on absolute buttons indices

AbstractSiriusSwtBotGefTestCase.getSectionButton() was too brittle as it
relied on the absolute position of buttons inside a group, which changed
with the addition of the new styles. Make the method more robust by
using SWTBot's buttonWithTooltipInGroup() API directly.

Bug: 424422
Change-Id: I062ea16042b6927bbee683f571229dce4d797035
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
3 files changed