AAPT2: always say which file failed to compile

Sometimes AAPT2 doesn't include the path of the file in the error
message, or just outputs a warning where an error should be printed
(but the overall build still fails without an error message). Let's
always include the file path to make it easier for the users to find out
the source of the failure.

Fixes: 122856772
Test: manual
Change-Id: Ibbbfd21b372792e5eaa40278186eb64cdfb0f60e
diff --git a/tools/aapt2/ResourceParser.cpp b/tools/aapt2/ResourceParser.cpp
index 58702dc..133cc84 100644
--- a/tools/aapt2/ResourceParser.cpp
+++ b/tools/aapt2/ResourceParser.cpp
@@ -714,7 +714,8 @@
     }
   }
 
-  diag_->Warn(DiagMessage(out_resource->source)
+  // If the resource type was not recognized, write the error and return false.
+  diag_->Error(DiagMessage(out_resource->source)
               << "unknown resource type '" << parser->element_name() << "'");
   return false;
 }