Deduplicate code in QueryMapper

[schauder]

Both the JDBC and the R2DBC module have a QueryMapper and a lot of code is duplicated between them. \

We should remove that code duplication, possibly by introducing a common super class.

[xeounxzxu]

@schauder

In the case of QueryMapper, I would like to comment on commonization.

QueryMapper is It has two properties: jdbc and r2dbc.

Write the common logic by abstracting it into the “spring-data-relational” module.

There are implementations of each jdbc and r2dbc.

In reality, I refer to the implementation for each property, but I think it would be better to improve maintainability by looking at the common implementation class.

What do you think?

• AbstractQueryMapper.class (module: spring-data-relational)
• JdbcQueryMapper.class (module: spring-data-jdbc)
• R2dbcQueryMapper.class (module: spring-data-r2dbc)