We're about to remove VertexShader, but we still care about types of
vertex attributes.

Bug: b/120799499

Change-Id: I80bed181479651e9d2470b81c7223e3381fbf4a7
Reviewed-on: https://swiftshader-review.googlesource.com/c/23708Tested-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>