When a struct was involved, the required size for each field was added
up, but also multiplied by its array size.  However, when calculating
the field size, the array size was already multipled in.

This resulted in the calculated size to be larger than it actually is,
resulting in failures in KHR-GLES31.core.compute_shader.shared-max.

Bug: angleproject:4173
Change-Id: I900c17fa65decdeb20c3651c3342295fed2f7c61
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1953483Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>