Backport missing MOB related changes to branch-2

While trying to backport https://issues.apache.org/jira/browse/HBASE-26969 to branch-2 I have found that multiple major MOB related changes are missing.

This change is required for FileBased SFT correctness so the changes it depends on should be backported first. Also any improvement to MOB stability is usually welcomed.

The missing changes I have found so far:
https://issues.apache.org/jira/browse/HBASE-22749
https://issues.apache.org/jira/browse/HBASE-23723
https://issues.apache.org/jira/browse/HBASE-24163

There is also a docs change describing the new MOB functionality. But considering that the book is always generated based on master I think it is safe to skip backporting it.
https://issues.apache.org/jira/browse/HBASE-23198

I'm planning to backport these changes one by one until we reach a state where HBASE-26969 can be backported too.