The MySQL and StarRocks column type mappings did not recognize the
`var_string` native type (returned for varchar-backed columns), so
these columns fell through unmatched and were not classified as
GenericDataType.STRING. As a result, controls that gate on column
type (e.g. the "Force categorical" / y-axis sort control) were
incorrectly hidden for such columns.
Add a `^var_string` regex mapping resolving to GenericDataType.STRING
in both engine specs, matching the workaround confirmed by the issue
reporter, plus regression cases in the parameterized column-spec tests.
Fixes#30282
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
f342aebe2a