Backport #98514 to 26.1: Fix unexpected result with read_in_order_use_virtual_row

[robot-ch-test-poll1]

Original pull-request #98514
Cherry-pick pull-request #98927

This pull-request is a last step of an automated backporting.
Treat it as a standard pull-request: look at the checks and resolve conflicts.
Merge it only if you intend to backport changes to the target branch, otherwise just close it.

The PR source

The PR is created in the CI job

---

Note

Medium Risk
Touches read-in-order/virtual-row query plan optimization, which can affect result ordering/correctness in JOIN+ORDER BY queries. Change is small but in a correctness-sensitive optimizer path.

Overview
Fixes virtual-row conversion generation for read_in_order_use_virtual_row by preserving the original ActionsDAG function node result_name when rebuilding monotonic expression chains (instead of auto-generating a new name).

Adds a stateless regression test (04001_virtual_row_conversions_join_column_names) covering ORDER BY on a casted low-cardinality key and JOIN conditions using Nullable subcolumns, including a full_sorting_merge join variant, to ensure stable/expected results.

^{Written by Cursor Bugbot for commit ad23ffc. This will update automatically on new commits. Configure here.}

[clickhouse-gh]

Workflow [BackportPR], commit [ad23ffc]

Summary: ✅