[PyQt] PyQtWebEngine build requirements

[Davide Pesavento]

Hi,

It seems that PyQtWebEngine 5.13.0 cannot be built with a version of
QtWebEngine older than 5.13.0 (see [1]). I was wondering if this
requirement is intentional given that, when the module was part of
PyQt5, it was compatible with a wide range of Qt versions.

Furthermore, does PyQtWebEngine version N require PyQt5 version >= N,
or there's no such requirement?

[1] https://bugs.gentoo.org/689602

Thanks,
Davide