Support for webOS's external OES sampler for video playback

We have an issue with qtwayland 6 which might need some help from Qt RnD.

In webOS video frames from the media pipeline are supposed to be handled with the external OES sampler, surface_oes_external.frag. And we found that it has been disabled in qtwayland 6, probably because there is an issue with compling it to .qsb format as mentioned in https://codereview.qt-project.org/c/qt/qtwayland/+/303874/6/src/compositor/shaders/compile#8.

As it is blocking video frame rendering in webOS, we have tried to compile it on our own but it is failing with errors below.

QSpirvCompiler: Failed to parse shader
Shader baking failed: ERROR: surface_oes_external.frag:16: 'texture' : no matching overloaded function found
ERROR: surface_oes_external.frag:16: 'assign' : cannot convert from ' temp highp float' to 'layout( location=0) out highp 4-component vector of float'
ERROR: surface_oes_external.frag:16: '' : compilation terminated
ERROR: 3 compilation errors. No code generated.

Could there be a resolution for this issue? Seems like Laszlo, the author of the patch above is already aware of this issue as mentioned in the commit message, and thus may have an idea.