Hide com.android.server package with @hide javadoc tag

Metalava currently doesn't respect @Hide annoation in package statement.
Use the old @hide javadoc tag there temporarily until the problem is
fixed.

Bug: 146466118
Test: m
Test: m after adding
@SystemApi(client=MODULE_LIBRARIES,client=SYSTEM_SERVER) to some of the
classes under frameworks/base/services

Exempt-From-Owner-Approval: cherry-pick from internal

Merged-In: I4af7380917fd2808bd6774b86fd4991485d6bfc6
(cherry picked from commit 5141f3790e)
Change-Id: I4af7380917fd2808bd6774b86fd4991485d6bfc6

services/core/java/com/android/server/package-info.java

@@ -13,5 +13,10 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
+/**
+ * @hide
+ * TODO(b/146466118) remove this javadoc tag
+ */
 @android.annotation.Hide
 package com.android.server;