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.cpp b/tools/aapt2/ConfigDescription.cpp
index 13f8b3b..c1697e7 100644
--- a/tools/aapt2/ConfigDescription.cpp
+++ b/tools/aapt2/ConfigDescription.cpp
@@ -783,4 +783,10 @@
     }
 }
 
+ConfigDescription ConfigDescription::copyWithoutSdkVersion() const {
+    ConfigDescription copy = *this;
+    copy.sdkVersion = 0;
+    return copy;
+}
+
 } // namespace aapt