Add partial Sort Operator #7456

Is your feature request related to a problem or challenge?

Consider a use case where required ordering is (a ASC,b ASC), and existing ordering is (a ASC).
As an example input is like following

expected output is like following

If we were to use information about existing ordering. We could buffer up a values until it changes like below

when 2 is received for the value of a. We could then sort subtable according to desired ordering (b ASC), then emit following result

I think this operator

• Enable us to use SortExec without breaking pipeline for some use cases (for this behavior we can write a new operator also).
• Decrease the memory usage of the SortExec when input ordering satisfy a prefix of the desired ordering.

Describe the solution you'd like

No response

Describe alternatives you've considered

This should be a new operator or current SortExec can be extended to behave this way.
However, I do think that extending current SortExec to behave this way is better option because:

• Existing plans will immediately benefit from this change (otherwise we need to write a rule to choose between SortExec and new PartialSortExec)
• less change will be introduced to code base. Since I presume, the two operators will have lots of code common anyway.

Additional context

See discussion for more background.