Allow mainline IPsec(IKE) to statically include @PolicyDirection

@PolicyDirection was hidden API defined in IpSecManager and
mainline module IPsec(IKE) needs to depend on it.

To remove this hidden API dependency, this commit:
- Moves definition of @PolicyDirection to a separate class
- Creates sharing filegroup framework-ike-shared-srcs for mainline
  IKE and include PolicyDirection.java

Bug: 146360859
Test: build, flash, boot
Test: atest FrameworksIkeTests
Change-Id: Ic6d7c06d4b92e16a9a65430365c9acc73932147b
diff --git a/Android.bp b/Android.bp
index 0612a53..96f5d7e 100644
--- a/Android.bp
+++ b/Android.bp
@@ -587,6 +587,14 @@
 }
 
 filegroup {
+    name: "framework-ike-shared-srcs",
+    visibility: ["//frameworks/opt/net/ike"],
+    srcs: [
+        "core/java/android/net/annotations/PolicyDirection.java",
+    ],
+}
+
+filegroup {
     name: "framework-networkstack-shared-srcs",
     srcs: [
         // TODO: remove these annotations as soon as we can use andoid.support.annotations.*