Enable Error Prone to detect obscure bugs.

We've been writing many new framework-specific Error Prone checkers
to help detect obscure platform bugs, and this change starts enabling
those checkers for more packages across the platform.

Bug: 155703208
Test: manual
Exempt-From-Owner-Approval: trivial blueprint changes
Change-Id: I9090b677a90d475b77b3d1127bb4e6c4e1201764

Android.bp

@@ -72,6 +72,7 @@ platform_compat_config {
 
 android_app {
     name: "Settings",
+    defaults: ["platform_app_defaults"],
     platform_apis: true,
     certificate: "platform",
     system_ext_specific: true,