Add new interfaces to enable virtual table to process IN operator constraints

all at once, rather than one element at a time.

FossilOrigin-Name: eb84b80e1f6d8c32bf0c9e1731f0233de0160a13f714f766779ae01fdf504e7b

src/whereInt.h

@@ -128,6 +128,7 @@ struct WhereLoop {
       i8 isOrdered;          /* True if satisfies ORDER BY */
       u16 omitMask;          /* Terms that may be omitted */
       char *idxStr;          /* Index identifier string */
+      u32 mHandleIn;         /* Terms to handle as IN(...) instead of == */
     } vtab;
   } u;
   u32 wsFlags;          /* WHERE_* flags describing the plan */