DEFINE_SIMPLE_STATE_EVENT: Add default constructor
DEFINE_SIMPLE_STATE_EVENT: Add default constructor

...that creates an "empty" event, i.e. an event with content initialised by a default constructor (not all content types support this but those for simple events do).

QMatrixClient/libqmatrixclient,QMatrixClient/libqmatrixclient,Fxrh/libqmatrixclient