Merge in CASA/casa6 from CAS-14143 to master
* commit '404299c4ede09576d22f0721b0103320933ad9f2':
CAS-14143 add type annotation to __convert_to_pol_selection
CAS-14143 refactoring for readability
added some comments
CAS-14143 add unit test for pol-dependent jyperk csv file
CAS-14143 properly handle pol-dependent Jy/K factor