Due to Debian policy the libkeymancore package will now include
the SONAME (API version number) in the package name (PR #10800). This
change adjusts the API verification checks to be able to cope with
the modified .symbols file.
If lines got removed in the .symbols file we won't find the current
version number in the .symbols file. This change fixes the expectations.
Also, if a major API change happens during the Alpha cycle we don't expect
another API version increment if one already happened since we released
the stable version.
This change also adds some unit tests for the new functionality. These
can be run manually and won't run during CI builds.
Fixes#10453.
