Add slices benchmark tests

Right now they just serialize and deserialize

Test: ./gradlew :slice-benchmark:connectedCheck
Change-Id: I59fcc14f630ebda452f58a4be8ab102eb97d9547
diff --git a/settings.gradle b/settings.gradle
index 1d7608d..fbbbd44 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -145,6 +145,7 @@
 includeProject(":slice-builders", "slices/builders")
 includeProject(":slice-test", "slices/test")
 includeProject(":slice-builders-ktx", "slices/builders/ktx")
+includeProject(":slice-benchmark", "slices/benchmark")
 includeProject(":slidingpanelayout", "slidingpanelayout")
 includeProject(":sqlite:sqlite", "persistence/db")
 includeProject(":sqlite:sqlite-ktx", "persistence/db/ktx")