CMake testing expect a fake_prefix folder resembling the installation prefix

When running unit tests for Android (probably the same for all cross-platform builds), CMake expects the fake_prefix folder at the root of the CMake tests build folder. For Android, the folder <qt_prefix>/src/ contains files needed for Android Gradle builds, without them apk generation won't work. For now, a workaround on Linux is to have a symbolic link from the actually installed qt prefix. 

The root cause is that androiddeployqt tries to copy the Gradle files from the fake_root where it should look in the qt install prefix

Cannot find template directory /home/assam/sources/qt5/qt5/qtbase/tests/build-tests/fake_prefix/src/3rdparty/gradle

the path is assigned by CMake  when generating  the JSON file in qtbase/src/corelib/Qt6AndroidMacros.cmake, we have this check

if (NOT QT_BUILDING_QT OR QT_STANDALONE_TEST_PATH)

that check for standalone var shouldn't be there and then, the value of qt_android_install_dir should be

set(qt_android_install_dir "${qt_path}")

instead of

set(qt_android_install_dir "${CMAKE_INSTALL_PREFIX}")