colexec: refactor CASE operator to support all types

Jesse Seldess (jseldess) commented:


PR: https://github.com/cockroachdb/cockroach/pull/66399

From release notes:
> The [vectorized execution engine](../v21.2/vectorized-execution.html] now supports `CASE` expressions that output `BYTES`-like types. [#66399][#66399) {% comment %}doc{% endcomment %}

Jira Issue: DOC-1389