Add Methane RHI integration in Qt Widgets

[egorodet]

According to discussion #144 it seems like there's a need to provide integration support for Qt Widgets. MethaneRhiWidget could serve as an alternative to QRhiWidget, which already exists in Qt 6.

This is an external feature request by @zhangfq-chemistry

[zhangfq-chemistry]

Please also provide QRhiWindow which is significantly efficient than QRhiWidget.

[zhangfq-chemistry]

Dear egorodet, there is an example called BGFX-Qt(https://github.com/theo-dep/bgfx-qt) you may follow.
Also, bkaradzic/bgfx#2846 may help.
Thanks!

[zhangfq-chemistry]

Would you like to add some basic primitives including cylinder, capsule, cone, line/dashed-line/dotted-line/polylines, polygon to Methane? Thanks a lot!