Migrate from AndroidManifest to build.gradle for namespace

AGP has deprecated use of packageName in AndroidManifest and
instead wants everyone to use `android { namespace = "foo" }`
in build.gradle files.

Test: ./gradlew tasks -> still passes
Change-Id: I4fa03cacc7214011f3797c36dcb76c2984c7bf52
diff --git a/paging/paging-guava/build.gradle b/paging/paging-guava/build.gradle
index 1a1b463..10a8b75 100644
--- a/paging/paging-guava/build.gradle
+++ b/paging/paging-guava/build.gradle
@@ -47,6 +47,10 @@
     legacyDisableKotlinStrictApiMode = true
 }
 
+android {
+    namespace "androidx.paging.guava"
+}
+
 // Allow usage of Kotlin's @OptIn.
 tasks.withType(KotlinCompile).configureEach {
     kotlinOptions {