SuperSize: Create, but don't yet use, one NativeSpec per-.so file

Reworks spec creation and abi-detection such that one NativeSpec is
created for each .so file. The extra specs are then ignored when
iterating them in order for this change to be a no-op.

Bug: 1193507
Change-Id: Iba58e1381138be72b49f6f389eb138520a8dce7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3371783


Reviewed-by: Samuel Huang <huangs@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/main@{#956779}