Avoid filegroup dependency from ICU to libcore.

The timezone_host_files filegroup was used to build the timezone-host
library in libcore. Since TzDataSetVersion.java in ICU depends on
libcore annotations and timezone-host doesn't add any libcore code that
depends on TzDataSetVersion.java, this topic reverses the dependency by
moving the timezone-host library to ICU. Libcore in the ART SDK instead
exports art.module.api.annotations that is needed to build
timezone-host.

Test: `m timezone-host` built entirely from sources and with
  art.module.api.annotations coming from the prebuilt produced by
  `build/soong/scripts/build-aml-prebuilts.sh art-module-host-exports`
Test: `m art-module-host-exports` on master-art (no ICU sources)
Bug: 172480615
Change-Id: Id7af8c859c0ddd2c06a200d07b8d039d9a754459
diff --git a/android_icu4j/Android.bp b/android_icu4j/Android.bp
index 2c5592a..6b4fcc8 100644
--- a/android_icu4j/Android.bp
+++ b/android_icu4j/Android.bp
@@ -61,15 +61,21 @@
     ],
 }
 
-// timezone-related source that is also used in host tests / tools and its
-// dependencies.
-filegroup {
-    name: "timezone_host_files",
+// A host library containing time zone related classes. Used for
+// host-side tools and tests that have to deal with Android
+// time zone data.
+java_library_host {
+    name: "timezone-host",
+    visibility: [
+        "//packages/modules/RuntimeI18n/apex",
+        "//system/timezone/distro/core",
+    ],
     srcs: [
         "libcore_bridge/src/java/com/android/i18n/timezone/TzDataSetVersion.java",
     ],
-    path: "libcore_bridge/src/java",
-    visibility: ["//libcore"],
+    libs: [
+        "art.module.api.annotations",
+    ],
 }
 
 // core-repackaged-icu4j contains only the repackaged ICU4J that does not