Delete the weighted-blended oit render target instead of destroying it


Destroying them only releases the native graphics objects, but not the
wrappers so those were leaked.

Pick-to: 6.12
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Change-Id: Ic1c5cd2ffeb2f36657ccf2f8e5a5be20bb584904
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
commitf2eb5bb12c6a452c09948b64c2be85baf911515b
parenta9f76f00eba02ff8494ab423fcd2b1dfbd60e4fa
authorAntti Määttä <antti.maatta@qt.io>
committerAntti Määttä <antti.maatta@qt.io>
commit timeThu, 1 Oct 2026 13:53:32 +0000