WifiNetworkSuggestion: Allow apps to provide granular suggestions

Allow apps to provide suggestions at the BSSID level for more fine
grained control.

Also,
a) Added some more documentation for
WifiNetworkConfigBuilder#buildNetworkSuggestion.
b) Added a missing match-none bssid pattern to validate.

Bug: 115504887
Test: ./frameworks/base/wifi/tests/runtests.sh
Change-Id: Ie551ea6753edba9bb0d05181390ab430f5510a63