Use type attributes in Brillo SELinux policy.

This way, the definition of the attribute is kept in a relevant file.

Also:
-Fold 'use_webservd' into the webservd_client attribute.
-Add a 'bidi_binder_call()' macro for domains that call each other over
binder.

Inspired by comments on
https://android-review.googlesource.com/#/c/197681/4/sepolicy/te_macros

Bug: 28209669
Change-Id: Ie95099bcc032360ed96244a6c91c5919f74af73e
11 files changed