@Keep all the things in TestAccessPointBuilder

The test in packages/apps/Settings/tests/unit/src/com/android/settings/
wifi/WifiSettingsUiTest.java fails because the TestAccessPointBuilder
class and all methods in it seem to get stripped during build time
since they aren't referenced by code within the settings app itself.

Bug: 33245941
Test: runtest --path packages/apps/Settings/tests/unit/src/com/android/settings/wifi/WifiSettingsUiTest.java
Change-Id: I92b56b7908e5be8a3553a2779646d48bb5b94f01