issue: #29892
This PR:
1. Move the process of gathering materialized search info to when the
search plan is created, before it goes to each segment, to avoid
repeated work and access the plan node under multi-threaded
circumstances.
2. Enforce the supported MV type to `VARCHAR`
3. Add integration test
Signed-off-by: Patrick Weizhi Xu <weizhi.xu@zilliz.com>
