Add automatic depth/shadow shaders for arbitrary materials

[NthTensor]

What problem does this solve or what need does it fill?

Allow depth to be correctly calculated for all materials, including StandardMaterials with AlphaMode::Mask and materials with custom vertex/fragment shaders.

Originally attempted in https://github.com/bevyengine/bevy/pull/5896, but implementation stalled. See that PR for suggested approach and reference.