Create flag for generated previews

Adds appwidget flag config to AConfigFlags.bp and create
FLAG_GENERATED_PREVIEW for generated preview work.

Bug: 308041327
Test: m android.appwidget.flags-aconfig-java
Change-Id: Ib6d27728a1cb9a0ad7493b456b24194f54a0a346

AconfigFlags.bp

@@ -63,6 +63,7 @@ aconfig_srcjars = [
     ":android.view.contentcapture.flags-aconfig-java{.generated_srcjars}",
     ":android.hardware.usb.flags-aconfig-java{.generated_srcjars}",
     ":android.tracing.flags-aconfig-java{.generated_srcjars}",
+    ":android.appwidget.flags-aconfig-java{.generated_srcjars}",
 ]
 
 filegroup {
@@ -722,3 +723,16 @@ java_aconfig_library {
     aconfig_declarations: "android.tracing.flags-aconfig",
     defaults: ["framework-minus-apex-aconfig-java-defaults"],
 }
+
+// App Widgets
+aconfig_declarations {
+    name: "android.appwidget.flags-aconfig",
+    package: "android.appwidget.flags",
+    srcs: ["core/java/android/appwidget/flags.aconfig"],
+}
+
+java_aconfig_library {
+    name: "android.appwidget.flags-aconfig-java",
+    aconfig_declarations: "android.appwidget.flags-aconfig",
+    defaults: ["framework-minus-apex-aconfig-java-defaults"],
+}

core/java/android/appwidget/flags.aconfig

+package: "android.appwidget.flags"
+
+flag {
+  name: "generated_previews"
+  namespace: "app_widgets"
+  description: "Enable support for generated previews in AppWidgetManager"
+  bug: "306546610"
+}