Permit non-struct, non-array types as buffers.

[jimblandy]

Fixes #2583.

[jimblandy]

Unfortunately, this is wrong, because the cube example breaks.

[jimblandy]

This is interesting:

[2022-04-07T05:38:28Z ERROR wgpu_hal::vulkan::instance] VALIDATION [UNASSIGNED-CoreValidation-Shader-InconsistentSpirv (0x6bbb14)]
    Validation Error: [ UNASSIGNED-CoreValidation-Shader-InconsistentSpirv ] Object 0: handle = 0x7f0f248b4160, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0x6bbb14 | SPIR-V module not valid: Structure id 21 decorated as Block must be explicitly laid out with MatrixStride decorations.
      %_struct_21 = OpTypeStruct %mat4v4float
    
[2022-04-07T05:38:28Z ERROR wgpu_hal::vulkan::instance] objects: (type: DEVICE, hndl: 0x7f0f248b4160, name: ?)
[2022-04-07T05:38:28Z ERROR wgpu_hal::vulkan::instance] VALIDATION [UNASSIGNED-CoreValidation-Shader-InconsistentSpirv (0x6bbb14)]
    Validation Error: [ UNASSIGNED-CoreValidation-Shader-InconsistentSpirv ] Object 0: handle = 0x7f0f248b4160, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0x6bbb14 | SPIR-V module not valid: Structure id 21 decorated as Block must be explicitly laid out with MatrixStride decorations.
      %_struct_21 = OpTypeStruct %mat4v4float

[jimblandy]

Work is proceeding here in gfx-rs/naga#1815.

[jimblandy]

With gfx-rs/naga#1815 and gfx-rs/naga#1823, this branch works.

[cwfitzgerald]

Something went real bad on CI here.

[jimblandy]

The CI failures seem to be gfx-rs/naga#1836 and gfx-rs/naga#1837.