The sorting algorithm didn't keep the fields in order, which made them
receive arbitrary locations.  The SPIR-V transformer assigns the
location on the whole block instead of individual members, which was
incorrect in this situation.

The SPIR-V transformer could have been modified to decorate each field
of the I/O block with a location.  This change instead sorts the fields
in such a way that I/O block fields are allocated contiguously, which
allows the SPIR-V transformer to function unchanged.

Bug: angleproject:3580
Change-Id: I27df9e8122dd4207835bad448ffb8015692a1635
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2581076Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>