Add apache-xml elements to the core APIs

See the associated change in external/apache-xml for
full details.

This change adds apache-xml source to the core_api_files
filegroup to include them in the core API files.

Bug: 113148576
Test: build
Change-Id: I2e2dbe15d675bd21b8e0a3a8c8e8763d254851fc
diff --git a/JavaLibrary.bp b/JavaLibrary.bp
index 9fdbf7f..07540b8 100644
--- a/JavaLibrary.bp
+++ b/JavaLibrary.bp
@@ -82,6 +82,7 @@
 filegroup {
     name: "core_api_files",
     srcs: [
+        ":apache-xml_api_files",
         ":bouncycastle_java_files",
         ":core_oj_api_files",
         ":core_libart_api_files",