Refactor TLSAA permission context to respect `persist` parameter

This doesn't change any behavior, since the permission context
previously explicitly bailed out of persisting non-ALLOW settings.
Writing the logic to only look at the `persist` parameter makes the
flow easier to reason about/debug.

This CL also makes a number of no-op refactorings to simplify
assertions and share code in the unit tests. (I'm happy to split
those into their own CL if you prefer.) It also adds a non-RWS unit
test that verifies the denial is not persisted.

Change-Id: I22926e02660a321ea0b1bc1181e2f6e67fccff8e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5718710
Reviewed-by: Shuran Huang <shuuran@chromium.org>
Commit-Queue: Chris Fredrickson <cfredric@chromium.org>
Auto-Submit: Chris Fredrickson <cfredric@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1329587}