Especially static inline variables. This greatly reduces the amount of
code that existed in macros, moving them to templates.
Additionally, this removes one level of indirection from
Q_APPLICATION_STATIC by removing the std::unique_ptr. We now directly
manage the object's storage.
Change-Id: I2cffe62afda945079b63fffd16bcc825cc04334e
Reviewed-by: Marc Mutz <marc.mutz@qt.io>