Support RLE DictionaryBlock.dictionary in UnnestingPositionsAppender

DictionaryBlock.dictionary will not be RLE in normal circumstances,
but since there is no precondition in the constructor, we cannot
rely on this to be always the case

core/trino-main/src/main/java/io/trino/operator/output/RleAwarePositionsAppender.java

@@ -54,7 +54,7 @@ public void append(IntArrayList positions, Block source)
     {
         // RleAwarePositionsAppender should be used with UnnestingPositionsAppender that makes sure
         // append is called only with flat block
-        checkArgument(!(source instanceof RunLengthEncodedBlock), "Append should be called with flat block but got %s", source);
+        checkArgument(!(source instanceof RunLengthEncodedBlock), "Append should be called with non-RLE block but got %s", source);
         switchToFlat();
         delegate.append(positions, source);
     }

core/trino-main/src/main/java/io/trino/operator/output/UnnestingPositionsAppender.java

@@ -117,6 +117,11 @@ public long getSizeInBytes()
     private void appendDictionary(IntArrayList positions, DictionaryBlock source)
     {
         Block dictionary = source.getDictionary();
+        if (dictionary instanceof RunLengthEncodedBlock rleDictionary) {
+            appendRle(rleDictionary.getValue(), positions.size());
+            return;
+        }
+
         IntArrayList dictionaryPositions = getDictionaryPositions(positions, source);
         if (dictionaryBlockBuilder.canAppend(dictionary)) {
             dictionaryBlockBuilder.append(dictionaryPositions, dictionary);