Separate LLNDK ABI diff reports from the other variants

- Soong generates the rules to compare prebuilts/abi-dumps/vndk and
  the intermediate dumps tagged with LLNDK.
- The LLNDK ABI diff report names contain ".llndk". Because LLNDK
  versioning has not been implemented, the reports are identical to
  those for NDK and PLATFORM.
- optInAbiDiff does not take isLlndkOrNdk as a parameter, as it is
  false for all known use cases.

Test: m libnativewindow
Bug: 314010764
Change-Id: I17097505472b9d6ab97a605f3f8dca8ea53d22c8