Disable multiview shader versions when xr is disabled

[clayjohn]

Partially addresses: #63217

This change disables colour passes that include Multiview when XR is disabled. This avoids compiling multiview variants of shaders when not using XR. Accordingly, non-XR users will not have shader compilation failures because their shader fails to compile for XR.

This PR does not fix- #63217 As the same problem will still arise for XR-users. When XR is enabled, the shader will still crash when using the NORMAL_ROUGHNESS_TEXTURE

[fire]

This breaks the usecase of multiview for looking glass displays, where in theory it can be accelerated for its 30ish multiviews.

[clayjohn]

This breaks the usecase of multiview for looking glass displays, where in theory it can be accelerated for its 30ish multiviews.

I'm not sure what you mean. Already we only support Multiview when XR is enabled, this just partially completes that by avoiding compiling shaders that will never be used.

[lyuma]

@fire I think that usecase can be addressed by having XR enabled in the renderer, but not necessarily using OpenXR. Note that other parts of godot already assume multiview is only used if XR is on.

[reduz]

I want to do this a bit different, lets talk about it during the week.

[clayjohn]

Closing as we will be going with a different (more complex, but much better) approach.

[BastiaanOlij]

I'd like to re-open this PR.

Seeing we originally implemented this solution from day 1 when multiview was introduced, it got broken at some point when we added all these new modes, and now we decided not to fix this months ago because of a change that Reduz suggests (a good change, don't get me wrong) that probably won't see the light of day until many months from now, possibly not until we get to it in 4.1 or 4.2, we have a problem with users now running into problems in 4.0.

Else I suggest we remove the logic that disables multiview shaders all together, if we've broken it and don't intent to fix it, then lets remove it so people who are doing XR don't keep falling into the pitfall of having to enable multiview shaders.

[akien-mga]

As discussed in the rendering channel, we agreed to merge this for now in 4.0.

[akien-mga]

Thanks!