[MSL] Metal Multi-View Rendering

When converting to MSL with multiview enabled, should amplification_id be used instead of layer rendering?

https://developer.apple.com/documentation/metal/render_passes/improving_rendering_performance_with_vertex_amplification?language=objc

Start with the linked Apple Metal documentation on vertex amplification and compare its amplification_id approach with the issue's current layer-rendering behavior. Determine the intended multiview semantics for MSL, then define the implementation scope and a regression test that demonstrates the accepted behavior.

Written by the indexing model from the issue text.