create appropriate logging extension

[atsushieno]

Currently we have logging.h which is not really an appropriate AAP extension. What it provides is a set of ugly C++ functions like a_log_f() which directly invokes android/log.h functions, which are of course not RT-safe.

It should be implemented like other host AAPXS-es i.e. the interface is queried by plugin (host "apps" do not need to provide the implementation though), the host AAPXS offers a function pointer, and when it is invoked it only dispatches the message and the arguments (before formatting, by some means?), then host actually logs it in another non-RT cycle.

[atsushieno]

There was an informative session at ADC-x SF https://youtu.be/fqWL2Qj5eSQ?t=2061