[Android] Show deprecation warnings for Android tests (flutter#31246)

Author: camsim99

shell/platform/android/test_runner/build.gradle

@@ -17,6 +17,13 @@ apply plugin: "com.android.library"
 
 rootProject.buildDir = project.property("build_dir")
 
+// Shows warnings for usage of deprecated API usages.
+gradle.projectsEvaluated {
+  tasks.withType(JavaCompile) {
+      options.compilerArgs << "-Xlint:deprecation"
+  }
+}
+
 def availableProcessors = Runtime.runtime.availableProcessors() ?: 1
 
 println "=========================================="