[feature](inverted index) support DROP INDEX ON PARTITION for inverted index

[airborne12]

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary:

Currently, DROP INDEX only supports table-level operations — it removes both the index metadata and physical index files across all partitions. In contrast, BUILD INDEX already supports partition-level operations via BUILD INDEX ON PARTITION.

This PR adds the corresponding inverse operation: DROP INDEX ON PARTITION, which deletes only the physical inverted index files on specified partitions while preserving the table-level index definition. This is useful for:

• Cleaning up index data on specific partitions to reclaim storage space
• Selectively removing indexes from cold/archive partitions while keeping them on hot partitions

Syntax:

-- Standalone form
DROP INDEX [IF EXISTS] idx_name ON table_name PARTITIONS (p1, p2, ...);

-- ALTER TABLE form
ALTER TABLE table_name DROP INDEX [IF EXISTS] idx_name PARTITION (p1);

Key design decisions:

• Only inverted indexes are supported (other index types are rejected)
• Table-level index metadata is NOT modified — the index definition remains in the schema
• Queries on affected partitions automatically fallback to non-index scan via enable_fallback_on_missing_inverted_index (default: true)
• Works in both storage-compute separation (cloud) and storage-compute integrated (local) modes
• No BE-side or cloud meta service changes required — reuses existing IndexChangeJob and buildOrDeleteTableInvertedIndices infrastructure

Release note

Support DROP INDEX ON PARTITION for inverted indexes, allowing users to delete physical index files on specified partitions without removing the table-level index definition.

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

• Behavior changed:

  • Yes. Added new SQL syntax DROP INDEX ... PARTITION/PARTITIONS (...) that was previously not supported. Existing DROP INDEX behavior without partition spec is unchanged.

• Does this need documentation?

  • Yes.

Check List (For Reviewer who merge this PR)

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

[Thearas]

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?

[airborne12]

run buildall

[airborne12]

run buildall

[hello-stephen]

FE UT Coverage Report

Increment line coverage 46.58% (34/73) 🎉
Increment coverage report
Complete coverage report

[airborne12]

run buildall

[airborne12]

run buildall

[github-actions]

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

[github-actions]

PR approved by anyone and no changes requested.

[eldenmoon]

LGTM