Reconcile `file_contexts` files for Release and Debug ART APEXes.

Replicate change
https://android-review.googlesource.com/c/1663786/2/apex/com.android.art-file_contexts
in `apex/com.android.art.debug-file_contexts`.

Test: Patch this commit into a tree that uses `artd` (only internal
      ones at the moment) and run the following command on a device
      running the Debug ART APEX:
        adb shell pm art \
          get-optimization-status com.google.android.youtube
Change-Id: If0b10b585778e8b585e76b2a4512a2f23facd22e
diff --git a/apex/com.android.art.debug-file_contexts b/apex/com.android.art.debug-file_contexts
index fa04b2f..cc60b70 100644
--- a/apex/com.android.art.debug-file_contexts
+++ b/apex/com.android.art.debug-file_contexts
@@ -3,6 +3,7 @@
 #
 (/.*)?                         u:object_r:system_file:s0
 /bin/art_exec                  u:object_r:art_exec_exec:s0
+/bin/artd                      u:object_r:artd_exec:s0
 /bin/dex2oat(d)?(32|64)?       u:object_r:dex2oat_exec:s0
 /bin/dexoptanalyzer(d)?        u:object_r:dexoptanalyzer_exec:s0
 /bin/odrefresh                 u:object_r:odrefresh_exec:s0