Fix shader compilation fail when using visibility range

[newDINO]

Objective

When using both deferred rendering and visibility range, shader pbr.wgsl can't be compiled because pbr_functions is not imported.

The issue can be reproduced by using DefaultOpaqueRendererMethod::deferred() and adding DeferredPrepass to camera at the visibility_range example.

Solution

Import pbr_functions when using PREPASS_PIPELINE.

Testing

I tested on visibility_range and deferred_rendering example. However, importing something usually doesn't break anything.

[NicoZweifel]

I was able to reproduce the issue in both examples and the PR fixes both examples.

One import at the top instead of in both blocks (#ifdef and #else) would be nice though.

[NicoZweifel]

I accidentally left some empty lines in the suggestions but looks good to go to me, thanks!