fix(android): lint on the predictive-back opt-in and the shared-art modifier

enableOnBackInvokedCallback only exists from API 33 and the app runs from
31, which lint reports as UnusedAttribute; tools:targetApi says that is
intended, since older releases ignore it. sharedArt becomes an extension
on Modifier, as Compose lint asks of modifier factories.

android/app/src/main/AndroidManifest.xml

@@ -12,6 +12,7 @@
         android:allowBackup="false"
         android:dataExtractionRules="@xml/data_extraction_rules"
         android:enableOnBackInvokedCallback="true"
+        tools:targetApi="33"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"
         android:supportsRtl="true"