[fix](load) fix broker load silently loaded only the first file when parsing multiple files path

[sollhui]

Proposed changes

Fix Nereids parsing for Broker Load statements that use multiple file paths in a single DATA INFILE clause, for example:

DATA INFILE("f1", "f2", "f3")

Previously, only the first file path was preserved. Later paths were parsed into a different ANTLR label and were not consumed by LogicalPlanBuilder, so Broker Load silently loaded only the first file.

This PR:

• Uses one ANTLR list label for all DATA INFILE paths.

• Updates LogicalPlanBuilder to build file paths from the collected list.

• Adds FE unit coverage for parsed file paths.

• Adds a regression case for S3 broker load with multiple paths in one DATA INFILE.

[hello-stephen]

Thank you for your contribution to Apache Doris.
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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?

[sollhui]

run buildall

[liaoxin01]

LGTM

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.