Android: improve a bit the "androiddeployqt is not smart and needs help" code
We do that by:
- Remembering all the generators we're building
- Linking the dependencies of all those generators against the app
For that to work we do three things:
- Move the creation of the app target to after the generator targets have been created
- Have a global variable that lists all the created generators
- Move the find_package of the generator dependencies to the top level so it can be used from the mobile app target