[C++][FlightRPC] Inconsistent use of int, int32_t, uint32_t for SqlInfo enum values

These should all be uint32_t, always. Not a big deal in practice at least.

**Reporter**: [David Li](https://issues.apache.org/jira/browse/ARROW-17558) / @lidavidm

_{**Note**: *This issue was originally created as [ARROW-17558](https://issues.apache.org/jira/browse/ARROW-17558). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

The issue points to the FlightRPC SqlInfo enum values; start by locating their C++ declarations and checking each value's type. Done means every SqlInfo enum value consistently uses uint32_t; no test or file path is named in the report.

Written by the indexing model from the issue text.