Project::targetExecutable: return path to the executable within an app bundle
Project::targetExecutable: return path to the executable within an app bundle

Certain applications rely on the full path to the executable in an app
bundle and cannot use the path of the bundle itself (e.g. lldb).
The qbs run command could use just the bundle path, because QProcess
contains magic to run app bundles.

Task-number: QTCREATORBUG-12833
Change-Id: I270acc141d0482f569e8d983e2d1382c7eb8994a
Reviewed-by: Jake Petroules <2d627e1cecd5435752fa500bacbe05f7cc90c369@petroules.com>

qt-labs/qbs,gatzka/qt-labs-qbs,villytiger/qbs,qtproject/qt-labs-qbs,villytiger/qbs,gatzka/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,villytiger/qbs,qt-labs/qbs,qt-labs/qbs,villytiger/qbs,Distrotech/qbs,Distrotech/qbs,gatzka/qt-labs-qbs,Distrotech/qbs,qt-labs/qbs,qt-labs/qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,Distrotech/qbs,Distrotech/qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,villytiger/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,villytiger/qbs,Distrotech/qbs,Distrotech/qbs,qt-labs/qbs