Wiring up the column statistics returned from the FileWriter by all…

…owing access to the footer in the `velox::dwrf::Writer`. (#10554)

Summary:
Pull Request resolved: #10554

The `FileWriter` now has a new getter for the footer.

Reviewed By: Yuhta

Differential Revision: D59924728

fbshipit-source-id: c0abd5cbb5ec75eb88e7c97b42414ec19032772e

velox/dwio/dwrf/writer/Writer.h

@@ -132,6 +132,10 @@ class Writer : public dwio::common::Writer {
     return writerBase_->getContext();
   }
 
+  const proto::Footer& getFooter() const {
+    return writerBase_->getFooter();
+  }
+
   WriterSink& getSink() {
     return writerBase_->getSink();
   }