QtGlobal: update docs after qglobal.h split

After moving the contents of qglobal.h to other headers (QTBUG-99313), some parts of documentation still remain in qglobal.cpp and are  marked with \relates <QtGlobal>.  Other docs are moved to proper locations (e.g. qnumeric.cpp, qlogging.cpp), but still retain \relates <QtGlobal>. Move the docs to correct .cpp/.qdoc files, and fix the \relates statements accordingly. Additionally, need to update the outdated description of QtGlobal, since now it mentions types, functions and macros that don't belong there anymore.