When creating materialized views, use REFRESH to load data.

When creating materialized views, use REFRESH to load data.

Previously, CREATE MATERIALIZED VIEW ... WITH DATA populated the MV
the same way as CREATE TABLE ... AS.

Instead, reuse the REFRESH logic, which locks down security-restricted
operations and restricts the search_path. This reduces the chance that
a subsequent refresh will fail.

Reported-by: Noah Misch
Backpatch-through: 17
Discussion: https://postgr.es/m/20240630222344.db.nmisch@google.com