branch-4.2 [fe](cse) Extract aggregate-argument CSE below distribute

[englefly]

Cherry-pick of #66815 to branch-4.2

fe Extract aggregate-argument CSE below distribute

The upstream patch refactors the inline CSE logic into a projectAggregateCse helper
(a cosmetic refactor that branch-4.2 does not have) and adds the new
PhysicalDistribute branch; the pick keeps branch-4.2's inline structure and adds the
behavioural change only.

branch-4.2 has no bucketed hash aggregate, so the new suite's
set enable_bucketed_hash_agg=false line was replaced by a comment; the remaining
plan and result checks pass on this branch (VEXCHANGE + VSELECT with 4 references to
the extracted cast(a as BIGINT) + cast(b as BIGINT) slot).

Testing: nereids_rules_p0/agg_strategy/cse_agg_distribute passes on a branch-4.2 FE.

[hello-stephen]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[englefly]

run buildall

[hello-stephen]

FE Regression Coverage Report

Increment line coverage 85.71% (24/28) 🎉
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