Support Wifi display devices that rename themselves.

Some Wifi display devices like to rename themselves after a
connection completes (or at other times).  Make sure to update
the name of the display when we detect that it changed in
our scan results.

This problem is somewhat complicated by the fact that we remember
the display name persistently, so we need to update our list
of remembered displays too.

Improve the state machine to avoid redundant attempts to
disconnect or cancel connection.

Bug: 7478895
Change-Id: I35a9e2c6a8deadbe892dacd5e3b4a5a2b12d6cf0