Support annotations for 'const'

It was not supported and people use type-level annotations as a
workaround even when the annotations are meant to annotate constants.

  const @Annotation... int foo = 0;

Now we can annotate constants like following.

  @Annotation... const int foo = 0;

Bug: 174436374
Test: aidl_unittests
Change-Id: I5481de6ac48711765fcd7e1726003267360ba9e6
2 files changed