Android emulator to CI for Qt 6

Who
As a Qt Android developer I want to verify my commits in CI e.g. in nightly builds.

What
Qt 6 shall support Android 28 as build-time and 23 as runtime https://intranet.qt.io/display/QTRD/Discussion+of+Qt+6.0%2C+6.1%2C+6.2+Supported+Functionality we should
Android target architectures and compilers: armeabi-v7a, arm64-v8a, x86, x86_64 (no changes) and compiler Clang 9 (no changes, same since r21). 
Android hosts architectures and compilers: Windows MinGW 8.1 (change), other platforms (no changes)
Why
For Qt5 to Qt6 there happens a BC break. There is significant changes to be done for Platforms Area e.g. https://bugreports.qt.io/browse/QTBUG-80233 and https://bugreports.qt.io/browse/QTBUG-84382
At the moment there is no CI supporting Android build in emulator. CI tests at the moment are empty, but report a success. Automatic tests are meaninful and do not provide false positives nor false negatives.

Definition of Done (DoD)
Android emulator support added to CI. CI builds Android for 28. CI provides results automatically from each build.

Proposed next steps/sub-tasks
-test with tests are valid
-enable and execute valid tests
-fix non-working valid tests

More info

• https://www.gsmarena.com/google_pixel_4-9896.php https://developer.android.com/about/versions/marshmallow/android-6.0