AAPT2: Warn when positional arguments exist and --legacy is on

This is normally an error, but old AAPT didn't check for it correctly,
so many projects violate this. With --legacy, this becomes a warning.

Change-Id: I23647e029930e11b719591cd38609e1b43247e20
diff --git a/tools/aapt2/ResourceParser.h b/tools/aapt2/ResourceParser.h
index 9ad749e..51cbbe1 100644
--- a/tools/aapt2/ResourceParser.h
+++ b/tools/aapt2/ResourceParser.h
@@ -44,6 +44,11 @@
      * Whether the default setting for this parser is to allow translation.
      */
     bool translatable = true;
+
+    /**
+     * Whether positional arguments in formatted strings are treated as errors or warnings.
+     */
+    bool errorOnPositionalArguments = true;
 };
 
 /*