This is just a refactoring which will allow adding a virtual getType()
method in a subsequent change without overload naming conflicts.

'isVoid()' has been removed since it appears unused now.

Bug: b/155302798
Change-Id: I16f5cbd947da9581e0f20837497f6b61cfeb7a21
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/45008
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>