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
diff --git a/aidl_checkapi.cpp b/aidl_checkapi.cpp
index b54ddbb..2b5664a 100644
--- a/aidl_checkapi.cpp
+++ b/aidl_checkapi.cpp
@@ -59,6 +59,7 @@
       AidlAnnotation::Type::BACKING,
       // @RustDerive doesn't affect read/write
       AidlAnnotation::Type::RUST_DERIVE,
+      AidlAnnotation::Type::SUPPRESS_WARNINGS,
   };
   vector<string> annotations;
   for (const AidlAnnotation& annotation : node.GetAnnotations()) {