feat: Fix legacy issue in index

[jiashenC]

• Remove secondary index maintained by ourselves. Instead, we now use IDMap provided by the FAISS library, which is also faster in terms of performance.
• Add support of creating index on UDF expression directly. Along with that, add udf signature as part of the index catalog, so the expression can be matched again when index is used later.

[xzdandy]

I'd like to get some context on adding support of creating index on UDF expression directly. For this case CREATE INDEX ON table (FeatureExtractor(col));, what is the expected index we want to create? Do we treat FeatureExtractor(col) as a table and create index on the feature extracted and store the mapping between the index and row_id?

[jiashenC]

I'd like to get some context on adding support of creating index on UDF expression directly. For this case CREATE INDEX ON table (FeatureExtractor(col));, what is the expected index we want to create? Do we treat FeatureExtractor(col) as a table and create index on the feature extracted and store the mapping between the index and row_id?

Yes, you are right.

[xzdandy]

I'd like to get some context on adding support of creating index on UDF expression directly. For this case CREATE INDEX ON table (FeatureExtractor(col));, what is the expected index we want to create? Do we treat FeatureExtractor(col) as a table and create index on the feature extracted and store the mapping between the index and row_id?

Yes, you are right.

Thanks. Overall LGTM.