Add the sqlite3_vtab_nochange() method which virtual table implementations

can use to optimize UPDATEs.

FossilOrigin-Name: d444b1ff39f0a1673a977b8047e1e14a49d461c9934be080d27c2392a830c1c0

src/vdbeInt.h

@@ -318,6 +318,7 @@ struct sqlite3_context {
   int isError;            /* Error code returned by the function. */
   u8 skipFlag;            /* Skip accumulator loading if true */
   u8 fErrorOrAux;         /* isError!=0 or pVdbe->pAuxData modified */
+  u8 bVtabNoChng;         /* Fetching an unchanging column in a vtab UPDATE */
   u8 argc;                /* Number of arguments */
   sqlite3_value *argv[1]; /* Argument set */
 };