Add @SuppressWarnings annotation

This only adds @SuppressWarnings annotation definition so that the AIDL
compiler understands it but does nothing about it yet.

The annotation has a single parameter named `value` of `String[]` type.

  @SuppressWarnings(value={".."})

It will suppress warnings(listed in `value` parameter) within the scope
of the annotated node.

Bug: 168028537
Test: aidl_unittests
Change-Id: Ic6bf4b023e882c8c97e0aeb629598bab6caf84de
4 files changed