Reduce dependencies during AOT contribution

[mp911de]

During AOT processing, we access the JdbcConverter which links to a DataSource caused by RelationResolver and NamedParameterJdbcOperations dependencies. We should instead obtain a RelationalMappingContext instance and fall back to JdbcCustomConversions to avoid access to a DataSource.

Data source access for JdbcDialect can be avoided by providing a JdbcDialect bean.