Allow creating triggers that reference unresolved columns

With the exception of columns in `new` and `old`, MySQL allows triggers that reference unresolved columns (TODO check if allowed for triggered table without `new`/`old` aliases).

Currently we allow triggers that reference unresolved tables (similar to MySQL) but we don't allow non-existent columns in resolved tables.

This is a similar issue to #10287.

Review the trigger-creation and column-resolution paths, using related issue #10287 as a starting point. Verify MySQL behavior for unresolved columns, including the `new`/`old` exception and the unresolved triggered-table case; done means valid triggers with unresolved columns are accepted without weakening those restrictions.

Written by the indexing model from the issue text.