AAPT2: Erase version qualifiers for resources <= minSdk

When resources share the same configuration, they are much more
clustered in the resulting resources.arsc, which makes for smaller
APKs. Strip version qualifiers for resources <= minSdk so that
they get clustered.

Bug:30050641
Change-Id: I80371b179761501fb7cc41f5f5ac67ffde2fc677
diff --git a/tools/aapt2/ConfigDescription.h b/tools/aapt2/ConfigDescription.h
index 5749816..ef0d147 100644
--- a/tools/aapt2/ConfigDescription.h
+++ b/tools/aapt2/ConfigDescription.h
@@ -65,6 +65,8 @@
     bool operator!=(const ConfigDescription& o) const;
     bool operator>=(const ConfigDescription& o) const;
     bool operator>(const ConfigDescription& o) const;
+
+    ConfigDescription copyWithoutSdkVersion() const;
 };
 
 inline ConfigDescription::ConfigDescription() {