Add a test-control to disable the skip-scan optimization.

FossilOrigin-Name: 650a3fe03d61068e06f3097878a777ca8ed713a769444cdb3f8be7d1e19a0b83

src/sqliteInt.h

@@ -1583,6 +1583,7 @@ struct sqlite3 {
    /* TH3 expects the Stat34  ^^^^^^ value to be 0x0800.  Don't change it */
 #define SQLITE_PushDown       0x1000   /* The push-down optimization */
 #define SQLITE_SimplifyJoin   0x2000   /* Convert LEFT JOIN to JOIN */
+#define SQLITE_SkipScan       0x4000   /* Skip-scans */
 #define SQLITE_AllOpts        0xffff   /* All optimizations */
 
 /*