Prepare T build rules for backwards compatibility

- Add a default to framework-connectivity-tiramisu for disabling
  T-only build rules.
- Separate the tiramisu hidden apis from hiddenapi txt files, so
  that the framework-connectivity-tiramisu file can avoid being
  referenced by the APEX when the JAR is not part of it.

Bug: 206893064
Test: m
Merged-In: I37c7385b456e4d71789aafe33cc8375adf40a681
Change-Id: I37c7385b456e4d71789aafe33cc8375adf40a681
diff --git a/Tethering/apex/Android.bp b/Tethering/apex/Android.bp
index c72d3a6..66efb8b 100644
--- a/Tethering/apex/Android.bp
+++ b/Tethering/apex/Android.bp
@@ -117,8 +117,13 @@
     // Additional hidden API flag files to override the defaults. This must only be
     // modified by the Soong or platform compat team.
     hidden_api: {
-        max_target_r_low_priority: ["hiddenapi/hiddenapi-max-target-r-loprio.txt"],
-        max_target_o_low_priority: ["hiddenapi/hiddenapi-max-target-o-low-priority.txt"],
+        max_target_r_low_priority: [
+            "hiddenapi/hiddenapi-max-target-r-loprio.txt",
+	],
+        max_target_o_low_priority: [
+            "hiddenapi/hiddenapi-max-target-o-low-priority.txt",
+            "hiddenapi/hiddenapi-max-target-o-low-priority-tiramisu.txt",
+	],
         unsupported: ["hiddenapi/hiddenapi-unsupported.txt"],
     },
 }