ContextualSearch API initial implementation

AconfigFlags.bp

core/api/system-current.txt

core/java/android/app/SystemServiceRegistry.java

...android/app/contextualsearch/ContextualSearchManager.java

...a/android/app/contextualsearch/ContextualSearchState.aidl

...a/android/app/contextualsearch/ContextualSearchState.java

...droid/app/contextualsearch/IContextualSearchCallback.aidl

...ndroid/app/contextualsearch/IContextualSearchManager.aidl

core/java/android/app/contextualsearch/flags.aconfig

core/java/android/content/Context.java

core/res/Android.bp

core/res/AndroidManifest.xml

services/Android.bp

services/contextualsearch/Android.bp

...rver/contextualsearch/ContextualSearchManagerService.java

...contextualsearch/ContextualSearchManagerShellCommand.java

services/java/com/android/server/SystemServer.java