* feat: add FTS support for Collection::CreateIndex/DropIndex
Enable dynamic creation and removal of FTS indexes on existing STRING
columns through the standard CreateIndex/DropIndex API, matching the
lifecycle model already used by vector and scalar (invert) indexes.
Key changes:
- New FtsIndexer class (fts_indexer.h/cc) encapsulating per-segment FTS
RocksDB management: multi-field lifecycle, snapshot, insert, seal
- New BlockType::FTS_INDEX with block_id-based directory naming
(fts.<block_id>.rocksdb) for crash-safe snapshot-and-swap
- Segment::create_fts_index builds FTS index on a snapshot copy by
scanning forward store, then outputs new SegmentMeta + FtsIndexer
for atomic reload (same pattern as create_scalar_index)
- Segment::drop_fts_index snapshots, removes field CFs, outputs updated
meta (or nullptr when last FTS field is removed)
- Collection layer wires FTS into the existing task dispatch, version
update, and reload loops alongside vector/invert paths
- CreateIndex/DropIndex reject unsupported index types explicitly
instead of falling through to the wrong branch
* fixup! feat: add FTS support for Collection::CreateIndex/DropIndex
fix: address review comments for FTS CreateIndex/DropIndex
- Reject CreateIndex when column already has a different index type
(e.g. FTS on an INVERT-indexed column) at both Collection and
Segment layers
- Allow same-type different-params CreateIndex to rebuild the index
(remove old + create new + replay data), aligned with INVERT behavior
- Return OK when CreateIndex is called with identical params
- Rename operator[] to get() in both FtsIndexer and InvertedIndexer
- Add test cases: create→drop→create→drop cycle, and params-change
rebuild with case-sensitivity verification
* android skip Feature_CreateOrDropFtsIndex
* fixup! feat: add FTS support for Collection::CreateIndex/DropIndex
443500dc45