OpImageQuerySize[Lod] SPIR-V instructions were previously implemented
by storing both the image depth and layer count in the descriptor. Since
3D textures can't be arrayed, we only need one field. Also avoid the
division by 6 for cube array layers in the instruction implementation,
by performing it during the descriptor update instead.

This reflects a similar change made by
https://swiftshader-review.googlesource.com/c/SwiftShader/+/47388

Bug: b/162315264
Change-Id: Iaa787e6c131eec2da7e4a404743ef722423305d5
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/47688
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>