fix: missing column comments after ALTER VIEW AS

[canbekley]

Resolves #1357

Split out from #1358 per maintainer request to land independently of the #1356 behavior change.

Description

When view_update_via_alter is enabled and the alter path issues ALTER VIEW <view> AS <query>,
Databricks silently drops every persisted column comment. The existing if column_comments block
in databricks__alter_view doesn't catch this because the column-comment diff is computed against
the pre-alter state — when model and existing comments match, the diff is empty, so nothing
reapplies them after ALTER VIEW AS wipes them.

Fix: inside the query branch of databricks__alter_view, reapply persisted column comments
after alter_query, gated on config.persist_column_docs() and model.columns. The pattern
mirrors databricks__persist_docs (dbt/include/databricks/macros/adapters/persist_docs.sql).

The existing if column_comments block is kept — it still handles the disjoint case where only a
column description changed in schema.yml (no query change, so the new reapply path doesn't run).

This fix becomes load-bearing once #1356 lands and ALTER VIEW AS runs on every invocation, but
the bug exists today on any query change and is worth fixing standalone.

Checklist

• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the CHANGELOG.md and added information about my change to the
  "dbt-databricks next" section.