Clarifies that the GL internal format is an "intended" format
and the Vulkan formats are "actual" formats. This makes all the format
fields use the same consistent naming pattern.

Bug: angleproject:5438
Change-Id: I935a49895109e9e06eae5ef98d5614dfd1128ff8
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2605728Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>