layers: Make passing a non-SPIRV shader to CreateShaderModule an error

layers: Make passing a non-SPIRV shader to CreateShaderModule an error

Various real drivers are not tolerant of the wrapped-GLSL-blob hack that
was used early in Vulkan development. Rather than simply bypassing most
of the validation when one of these blobs is seen, make it an error.

Structurally, move the validation out of the shader_module ctor in
preparation for the callback being able to signal whether to bail out.

V2: Adjustment for descriptor validation landing

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Tobin Ehlis <tobin@lunarg.com>