HIVE-27000: Improve the modularity of the *ColumnStatsMerger classes

[asolimando]

What changes were proposed in this pull request?

Improving the modularity of the *ColumnStatsMerger classes by introducing a common parent class and moving there all the shared code that is not depending on the data type.

Why are the changes needed?

Those classes host some complex merging logic that is copy-pasted into several classes, a problem that is bound to worsen as we add new (and more complex) statistics.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Existing and introduced unit-tests relevant for the change:
mvn test -Dtest.groups=org.apache.hadoop.hive.metastore.annotation.MetastoreUnitTest -Dtest='*ColumnStats*Test.java' -pl standalone-metastore/metastore-server

[sonarqubecloud]

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0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

No Coverage information
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[akshat0395]

LGTM, +1

[asolimando]

@ayushtkn, if you have spare cycles maybe you can help get this in since it's been approved already? Thanks!

[ayushtkn]

LGTM.
Will give a day before committing in case anyone else has comments

[ayushtkn]

And I messed up while committing :-(
Forgot to mention Akshat's name while committing, Have reverted this and committed it again with the correct message. I don't have anything more than sorry here, will be more careful next time

[asolimando]

And I messed up while committing :-( Forgot to mention Akshat's name while committing, Have reverted this and committed it again with the correct message. I don't have anything more than sorry here, will be more careful next time

We never make mistakes only if we do nothing at all, you are very very active so it happens. On that note, thanks a lot for always helping out with reviews and merges, much appreciated Ayush!