Build system: Support Qt (git) module wide properties

With https://codereview.qt-project.org/c/qt/qtbase/+/331201, we can add global defines and disable them for specific targets, which is already quite useful.

However, it would be nice if there was a way to add such global properties only in modules which opt-in into using them: E.g. qtbase and qtdeclarative opt-in, and the property gets set on all targets there, but it does not get set in qtmultimedia, quick3d, etc.

A use-case for this feature would be introducing source breaking changes into a non-leaf module, but hiding the breakage via defines. E.g. https://codereview.qt-project.org/c/qt/qtbase/+/394301 could use it to still provide the removed includes, unless modules claim that they have fixed any breakage.