Allow users to opt-out of exotic calendars

qromancalendar_data_p.h, qhijricalendar_data_p.h are one of the biggest files in qtbase/src/core:

$ find . -type f -printf "%k %p\n" | sort -hr | head -10
2396 ./mimetypes/mime/packages/freedesktop.org.xml
1108 ./text/qunicodetables.cpp
700 ./text/qlocale_data_p.h
344 ./time/qromancalendar_data_p.h
324 ./text/qstring.cpp
200 ./kernel/qobject.cpp
192 ./time/qdatetime.cpp
160 ./time/qhijricalendar_data_p.h
160 ./text/qbytearray.cpp
148 ./text/qlocale.cpp

I haven't measured the impact on binary size, but I expect it to be significant.

We should therefore allow people who are after a truely minimal Qt to opt out of these calendars, for instance with a -no-feature-calendar flag, or -no-feature-roman-calendar, -no-feature-ijri-calendar flags.