Add support for table name placeholder for `@Query` in JDBC and R2DBC

[mipo256]

Currently, there is no way to reference the name of the table in the SPEL expression in @Query. The behavior I guess should be similar to one we have now in JPA. So something like this:

@Query("SELECT * FROM #{#tableName} WHERE status = #{#status.name()}")
List<MyEntity> findByStatus(Status status);

I think would be the way to go.

[mp911de]

Table-name pre-processing requires an additional step to resolve expressions inline without binding these as parameters. The table name would be rendered in its final form meaning with quotation.

[schauder]

And I guess we would need to parse the whole thing first to determine, which expression we must process with inline String replacement and which become parameters.

[mp911de]

JPA does something along the lines of `String.replace("#{#entityName}}", …)" which is pretty isolated and it doesn't introduce much of additional injection risks.

[mipo256]

@mp911de Maybe I'm wrong, but in JPA the entityName is just added as an additional variable into Evaluation context. I guess this is better then just doing String.replace()...

[mp911de]

renderQueryIfExpressionOrReturnQuery runs the entire query through SpEL parsing and expression processing.

The actual SpEL evaluation (and parsing) for parameter values happens here:

https://github.com/spring-projects/spring-data-jpa/blob/5f924440b78f85862d83f978fdbeda10973b42eb/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/QueryParameterSetterFactory.java#L185-L211