Simplify InlineSwitchPayloads and generalize get/set method

InlineSwitchPayload now assumes that all switches will be
stored as 1 or 0, which simplifies the code.

Moves Availability into ResultPayload, so that custom
payloads can be created to set/get values which are more
complicated than stotring ints (like bluetooth or DnD),
and give more expressive reasons when unavailable.

Bug: 62022517
Test: make RunSettingsRoboTests
Change-Id: I87e6fc041bfd398e7daf6e6e479d502930d36f0f

src/com/android/settings/search/DatabaseIndexingManager.java

@@ -803,6 +803,7 @@ public class DatabaseIndexingManager {
                         entries = XmlParserUtils.getDataEntries(context, attrs);
                     }
 
+                    // TODO (b/62254931) index primitives instead of payload
                     payload = DatabaseIndexingUtils.getPayloadFromUriMap(controllerUriMap, key);
                     childFragment = XmlParserUtils.getDataChildFragment(context, attrs);