[Format] Query cancellation and progress

[lidavidm]

Executing a query requires blocking and waiting for results to be available. This is imperfect:

• There's no way for a client to cancel query execution.
• There's no way to get query progress. APIs like JDBC don't support this (nor do databases like PostgreSQL), but vendors like BigQuery and Snowflake do support this. (OLTP use cases often consider long queries a problem, but OLAP queries are expected to take a while.)

Proposal

• Add AdbcStatementCancelExecution. This is explicitly a thread-safe operation.
• Clarify that releasing an ArrowArrayStream early should mean cancellation of the underlying query when returned from ExecuteQuery, but not when returned from ReadPartition.
• Add AdbcStatementGetDouble(struct AdbcStatement*, const char*, double*) and a corresponding string constant to retrieve query progress information. (This is also explicitly thread-safe.)

Open Questions

• Should we go ahead and add a full complement of Get/SetFoo functions for all objects right now to avoid further ABI changes in the future? We could then also expose things like the proposed result set expiration and the endpoints_ordered flag from Flight SQL.