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_language.h b/aidl_language.h
index 9bcbaa9..112c6dc 100644
--- a/aidl_language.h
+++ b/aidl_language.h
@@ -171,6 +171,7 @@
     FIXED_SIZE,
     DESCRIPTOR,
     RUST_DERIVE,
+    SUPPRESS_WARNINGS,
   };
   static std::string TypeToString(Type type);
 
@@ -260,6 +261,7 @@
   const AidlAnnotation* UnsupportedAppUsage() const;
   const AidlAnnotation* RustDerive() const;
   const AidlAnnotation* BackingType() const;
+  std::vector<std::string> SuppressWarnings() const;
 
   // ToString is for dumping AIDL.
   // Returns string representation of annotations.