Android: Qt6 compatibility

[hoffie]

What is the current behaviour and why should it be changed?

Jamulus will fail to build with Qt6 even when #2299 is merged as it uses androidextras for permission handling, which is no longer available.

Describe possible approaches

1. Stay on unsupported Qt 5.15.2
2. Use the private implementation when building against Qt6 as described in the relevant Qt ticket

I'd go with (2), although it is not nice either.

Has this feature been discussed and generally agreed?

No.

[pljones]

I've no desire to move off 5.15.2.

[ann0see]

There's probably mostly a need for other OS which have potential (security) issues.

[pljones]

Moving to 3.9.1 along with the other Android ticket.