Add SQL scalar function rtreecheck() to the rtree module. For running checks

to ensure the shadow tables used by an rtree virtual table are internally
consistent.

FossilOrigin-Name: dde0bb3eab1316c3247b1755594527ca70955aab4ad4907190731f7ec092b327

ext/rtree/rtree1.test

@@ -519,7 +519,7 @@ foreach {tn sql_template testdata} {
     do_test $testname.2 [list sql_uses_stmt db $sql] $uses
     do_execsql_test $testname.3 { SELECT * FROM t1 ORDER BY idx } $data
 
-    do_test $testname.4 { rtree_check db t1 } 0
+    do_rtree_integrity_test $testname.4 t1
     db close
   }
 }