Prior to this change, the OpenGL compiler accepted all "non-struct"
"non-array" types for unary operations (++, --, and -). This ignored
the existence of sampler objects. If someone tried to negate a
sampler, then the compiler would tell the assembler to negate a non-
numerical type.

This change makes it so the GSL compiler only accepts unary operations
on numerical types (including vectors and matrices).

Also added a unittest that makes sure we gracefully fail to compile
bad unary operations.

Bug chromium:910883

Change-Id: Ia69056b31664900c3126cab42ecb8603d1a5d7db
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/32448Tested-by: Sean Risser <srisser@google.com>
Presubmit-Ready: Sean Risser <srisser@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>