Add `DevToolsR2dbcAutoConfiguration` to automatically shutdown in-memory
R2DBC databases before restarting. Prior to this commit, restarts that
involved SQL initialization scripts could fail due to dirty database
content.
The `DevToolsR2dbcAutoConfiguration` class is similar in design to
`DevToolsDataSourceAutoConfiguration`, but it applies to both pooled
and non-pooled connection factories. The `DataSource` variant does not
need to deal with non-pooled connections due to the fact that
`EmbeddedDataSourceConfiguration` calls `EmbeddedDatabase.shutdown`
as a `destroyMethod`. With R2DB we don't have an `EmbeddedDatabase`
equivalent so we can always trigger a shutdown for devtools.
Fixes gh-28345
b93a629dbe