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
Ignore-AOSP-First: Merge conflict. Cherry-pick to aosp afterwards
Change-Id: I37c7385b456e4d71789aafe33cc8375adf40a681
4 files changed