spirv-val: Check that push constants are not decorated with binding / set locations

Spawned from https://github.com/KhronosGroup/glslang/issues/1367 --- binding and set decorations are not allowed in push constants. This doesn't seem to be verified by spirv-val currently.

Start with the spirv-val entry point and trace its existing validation for push constants and binding/set decorations. Verify that push constants carrying either decoration are rejected; completion means the validator enforces this rule.

Written by the indexing model from the issue text.