Add PagedSource.Factory + LiveData implementation

Test: ./gradlew paging:paging-common:check
Test: ./gradlew paging:paging-runtime:cC
Change-Id: Ie481faad6b0a2756f896d7fbc1f6d8152ddebcdc

diff --git a/paging/common/api/current.txt b/paging/common/api/current.txt
index 8c69383..9e3841a 100644
--- a/paging/common/api/current.txt
+++ b/paging/common/api/current.txt

@@ -246,6 +246,8 @@
     method public void invalidate();
     method public abstract boolean isRetryableError(Throwable error);
     method public abstract suspend Object load(androidx.paging.PagedSource.LoadParams<Key> params, kotlin.coroutines.Continuation<? super androidx.paging.PagedSource.LoadResult<Key,Value>> p);
+    method public final void registerInvalidatedCallback(kotlin.jvm.functions.Function0<kotlin.Unit> onInvalidatedCallback);
+    method public final void unregisterInvalidatedCallback(kotlin.jvm.functions.Function0<kotlin.Unit> onInvalidatedCallback);
     property public final boolean invalid;
     property public abstract androidx.paging.PagedSource.KeyProvider<Key,Value> keyProvider;
   }
@@ -309,6 +311,10 @@
     enum_constant public static final androidx.paging.PagedSource.LoadType START;
   }
 
+  public final class PagedSourceKt {
+    ctor public PagedSourceKt();
+  }
+
   public abstract class PositionalDataSource<T> extends androidx.paging.DataSource<java.lang.Integer,T> {
     ctor public PositionalDataSource();
     method public static final int computeInitialLoadPosition(androidx.paging.PositionalDataSource.LoadInitialParams params, int totalCount);