Fix copyPreserveEncodings for LazyVector (#11855)

Summary:
Pull Request resolved: #11855

When loading data without a predicate we can the hive connector can return some LazyVectors. Currently the data sink attempts a call to copyPreserveEncodings (which is unsupported by LazyVector) to get a long lived owned copy of the data against its own memory pool. Putting this aside, we actually want to see impulse preload this data ahead of time for reliable query perf.

This diff patches LazyVector::copyPreserveEncodings and ensures Impulse preloads data prior to obtaining a copy.

Reviewed By: Yuhta

Differential Revision: D67204919

fbshipit-source-id: 189a0877824872f355c5a7677be0219318722460

velox/vector/LazyVector.h

@@ -364,8 +364,9 @@ class LazyVector : public BaseVector {
   void validate(const VectorValidateOptions& options) const override;
 
   VectorPtr copyPreserveEncodings(
-      velox::memory::MemoryPool* /* pool */ = nullptr) const override {
-    VELOX_UNSUPPORTED("copyPreserveEncodings not defined for LazyVector");
+      velox::memory::MemoryPool* pool = nullptr) const override {
+    VELOX_CHECK(isLoaded());
+    return loadedVector()->copyPreserveEncodings(pool);
   }
 
  private: