Cleared confusion between GL level indices and VK level indices by
adding the corresponding suffix to variables and function arguments.  A
handful of places that sent one index and expected the other are fixed.

A couple more places needed this adjustment that were missed in the
first CL. Also included a test to provoke those situations.

The conversion between the two is given by:

    levelIndexGL = levelIndexVk + baseLevel;

Bug: angleproject:4695
Change-Id: I3b8e5699abee1b011e52b666e6e245f44cb8ad6f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2302549Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>