Consider splitting macros into cxx-qt-macro, so that reexport and docs can work

[ahayzen-kdab]

Split macros into cxx-qt-macro then reexport in cxx-qt so that we can cxx_qt::QObject a struct in the cxx_qt definition (see https://users.rust-lang.org/t/solved-is-it-possible-to-reexport-a-proc-macro/16864 )

[ahayzen-kdab]

The docs now work (#456) and we don't use cxx_qt::QObject anymore we use qobject::T, so we don't need to try and reexport QObject from cxx-qt anymore, therefore closing,