Fix a performance regression: Keep two btree masks in each prepared

statement; one for btrees used and another for btrees that require locks.
Only try to lock the btrees identified by the second mask.

FossilOrigin-Name: 614de91a504d2231009a9de1305e31fce1b1c5a6

src/vdbeInt.h

@@ -303,6 +303,7 @@ struct Vdbe {
   u8 isPrepareV2;         /* True if prepared with prepare_v2() */
   int nChange;            /* Number of db changes made since last reset */
   yDbMask btreeMask;      /* Bitmask of db->aDb[] entries referenced */
+  yDbMask lockMask;       /* Subset of btreeMask that requires a lock */
   int iStatement;         /* Statement number (or 0 if has not opened stmt) */
   int aCounter[3];        /* Counters used by sqlite3_stmt_status() */
 #ifndef SQLITE_OMIT_TRACE