Inconsistent handling of enums and flags in the Qt namespace

There is wide variation in how enums and flags are handled in the Qt namespace. For example:

• QT_Q_FLAG(SplitBehavior): this seems to follow QTBUG-77216 (Q_FLAG on the enum itself)
• QT_Q_FLAG(MouseButtons): this uses the macro on the flags rather than the enum itself
• QT_Q_ENUM(WindowState) and QT_Q_FLAG(WindowStates): this uses the macro on both, which is somewhat unclear given the advice of Q_FLAG documentation ("The Q_FLAG macro takes care of registering individual flag values with the meta-object system, so it is unnecessary to use Q_ENUM() in addition to this macro.")

The end result is inconsistency in using these with the metatype/metaobject system. For example:

qMetaTypeId<Qt::MouseButtons>() // okay
qMetaTypeId<Qt::MouseButton>() // not okay