Wifi usability: Add @SystemApi to receive Wifi usability score

Add system API to allow framework to receive Wifi usability score from system APK.
Also add a new permission to protect this API from being used by unauthorized applications. This permission is the same as the one added for sending Wifi usability stats.

Bug: 113262380.

Test: frameworks/base/wifi/tests/runtests.sh

Signed-off-by: Mingguang Xu <mingguangxu@google.com>

Change-Id: Ib695dbb4c6c1f4518a464877f1d0f60dde4904eb