This also moves ANGLE_INSTANTIATE_TEST to its own header and makes it
generic over the type of test parameter.

BUG=angleproject:892

Change-Id: Id4e3929d7ad06964b3259015915be84a8ee414f9
Reviewed-on: https://chromium-review.googlesource.com/272553Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>