Add a test that checks index creation on expression

[Ngalstyan4]

Test the case when the table does not have a vector column but an hnsw index is create on an expression-generated vector

something like

CREATE INDEX ON papers(clip_text(abstract));

context:
https://www.postgresqltutorial.com/postgresql-indexes/postgresql-index-on-expression/

[dqii]

I wrote this test -- there seems to be a bug though