Add dynamic summaries to Slices

Summary on slices will now determined by checking that
summaries in the following order are valid:
1) SliceData summary
2) Preference Controller summary
3) SliceData screen title

Valid is currently defined as:
- Not empty / null
- Not whitespace
- Not sumamry placeholder

Fixes: 71640678
Test: robotests
Change-Id: I5e699e8566ece80742d311617b7dc4e9a9bda8cf

src/com/android/settings/slices/SliceDataConverter.java

@@ -163,7 +163,7 @@ class SliceDataConverter {
 
                 // TODO (b/67996923) Non-controller Slices should become intent-only slices.
                 // Note that without a controller, dynamic summaries are impossible.
-                // TODO (b/67996923) This will not work if preferences have nested intens:
+                // TODO (b/67996923) This will not work if preferences have nested intents:
                 // <pref ....>
                 //      <intent action="blab"/> </pref>
                 controllerClassName = XmlParserUtils.getController(mContext, attrs);