MultimediaQuick: QSGVideoMaterial / QSGVideoNode improvements


* declare classes as final
* declare const members const

Pick-to: 6.12
Change-Id: Id5cca22f5cf5bab7864cccfbdb1c526614d092e9
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
commit9ddaf83271725dc308a1aa3d993fbdd7658ca622
parent69cc21dbe261ce555fec44be19058866a89dc5d1
authorTim Blechmann <tim.blechmann@qt.io>
committerTim Blechmann <tim.blechmann@qt.io>
commit timeWed, 21 Oct 2026 13:19:38 +0000