Enable CLIENT_FOUND_ROWS in r2dbc-mysql in favor of spring-data-r2dbc

[ks-yim]

After spring-projects/spring-data-r2dbc#253, spring-data-r2dbc assumes CLIENT_FOUND_ROWS capability flag is enabled for its mysql connections.

This causes a problem with jasync-r2dbc-mysql as a backing driver for spring-data-r2dbc when we try to save an unchanged entity...:

val fooRepository: R2dbcRepository<FooEntity, Int>

// throws an exception since `affectedRows` evaluates to 0 in MySQL without `CLIENT_FOUND_ROWS` flag.
fooRepository.save(fooRepository.findById(1))

It would be nice if there's an option to enable CLIENT_FOUND_ROWS flag in MySqlConnection.kt to enable it in MySqlConnectionFactoryProvider#create.

[github-actions]

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[oshai]

Thanks for raising the issue. I'll need to investigate how to implement that, and will try to do that when possible.

[ks-yim]

It seems there's no easy way of overriding capability flags. We can add related properties to Configuration class but it feels awkward since they only have meanings in MySQL context.

One potential hack is to detect a spring-data-r2dbc(or R2DBC) related class in the classpath and cache the result upon class loading and conditionally enable CLIENT_FOUND_FOWS flag depending on the result.

[oshai]

created PR #247

[oshai]

Fix is in version 1.2.3.

[ks-yim]

Thanks!