licheck should not be interactive

licheck interacts with the user. this poses integration problems with the surrounding configure script, as that one would like to redirect all output (see QTBUG-61017). it also mostly duplicates the input logic configure has for the opensource license anyway.

it would be much cleaner if licheck was limited to decoding and validating the license, and reporting the relevant output in form of assignments like after successful validation.
the separate mode used for invocation from default_pre.prf should be unified with that as well.