branch-4.1: [feature](fe) Support ANN indexes on MoW tables

[airborne12]

What problem does this PR solve?

Issue Number: N/A

Related PR: #61994

Problem Summary:
This backports ANN index support for unique-key merge-on-write tables to branch-4.1. FE validation previously restricted ANN indexes to DUP_KEYS tables even though merge-on-write scans filter deleted rows before ANN candidates are evaluated. The change permits ANN indexes only for UNIQUE_KEYS tables with merge-on-write enabled, preserves rejection for merge-on-read tables, and covers both the Nereids and legacy branch-4.1 CREATE INDEX validation paths.

Release note

Support ANN indexes on unique-key merge-on-write tables.

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason
  • Verification:
    • ORC_FORMAT_URL=http://archive.apache.org/dist/orc/orc-format-1.0.0/orc-format-1.0.0.tar.gz ./build.sh --be --fe -j 160
    • ./run-fe-ut.sh --run org.apache.doris.nereids.trees.plans.commands.IndexDefinitionTest,org.apache.doris.alter.SchemaChangeHandlerTest
    • ./run-regression-test.sh --run -d ann_index_p0 -s ann_index_on_mow,build_ann_index_test,create_ann_index_test,create_tbl_with_ann_index_test -parallel 4

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

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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?

[airborne12]

run buildall