pyqt: Updated formula with Python 3 support

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

pyqt: Added --sip-incdir option

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

pyqt: Ugly hack to work around brew bot's problems with if else deps

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Removed ugly hack, changed how PYTHONPATH is added.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

pyqt: Changed PYTHONPATH setting

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

pyqt: Fixed PYTHONPATH in test method

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

pyqt: More PYTHONPATH tweaking

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

pyqt: Tweaked PYTHONPATH again

Closes #26510.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

WIP