iwa: Modify Permissions Policy to support a visibility feature

This change allows permissions policy to ensure that visibility
of a feature is dependent on whether the execution context is
isolated, as defined in the json5 file for each of the features.

As part of this change, also mark the following permissions
policy entries as visible only to execution contexts that are
isolated:
- direct-sockets
- smart-card
- sub-apps
- web-printing

Bug: b/320681780, b/40191772
Change-Id: I2364f1ac6a97fbe0ede851d6eaeabfc9559d85b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5503309
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Commit-Queue: Chase Phillips <cmp@chromium.org>
Auto-Submit: Chase Phillips <cmp@chromium.org>
Reviewed-by: Robbie McElrath <rmcelrath@chromium.org>
Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1302752}