This commit introduces the bare minimum cmake support that should
unblock the CI and allow further verification and development on most
platforms: macOS, Linux, Win, iOS and Android.
* The support for sensorfw backend is very preliminary and can
be enabled later if needed (no Qt6 version of the sensorfw).
* The simulator backend is dropped as obsolete / unnecessary.
* Three examples are currently commented out and shall be ported with
a later commit.
Reviewed-by: Alexandru Croitor <email@example.com>