Add an optimization that attempts to run a subquery as a coroutine rather

than manifesting it into a temporary table.

FossilOrigin-Name: 7af3acbbd49a2114fcdada9ec907c68ba9b053bd

src/vdbeInt.h

@@ -63,6 +63,7 @@ struct VdbeCursor {
   Bool isIndex;         /* True if an index containing keys only - no data */
   Bool isOrdered;       /* True if the underlying table is BTREE_UNORDERED */
   Bool isSorter;        /* True if a new-style sorter */
+  Bool multiPseudo;     /* Multi-register pseudo-cursor */
   sqlite3_vtab_cursor *pVtabCursor;  /* The cursor for a virtual table */
   const sqlite3_module *pModule;     /* Module for cursor pVtabCursor */
   i64 seqCount;         /* Sequence counter */