Develop some test and/or tools for RQG for covering maybe faulty maintenance of indexes

During fixing MDEV-20066 it turned out that

- the basic mistake in code leads to some wrong maintenance of the clustered index

- at least the SQL revealing the defect isn't that complicated

  CHECK TABLE or

  enforce to get result sets based on SELECT ... FORCE INDEX ... etc. and compare them

The Standard RQG Testsuite for checking InnoDB is able to catch MDEV-20066 (assert

reported on top of bug report) but that is rather some of the probably various sideeffects

of the basic mistake. The suite might be capable to catch also the basic bug direct.

But caused by the frequent table rebuilds caused by DDL the likelihood to catch that

is very low.

Some of the RQG optimizer tests might be capable to catch MDEV-20066 or the base bug too. But running them are a not acceptable overhead  for covering InnoDB functionality only.

So the task here is:

1. Figure out a way to catch the basic bug below MDEV-20066 with RQG,  short total runtime

     and small manual analysis.

2. Modify that so that ANY faulty maintenance of clustered index or secondary indexes

    get caught.

3. Extend the Standard RQG Testsuite