propose @DialectOverride annotation

[gavinking]

This allows the use of native SQL in annotations of portable programs.

We've needed something like this for a long time.

[gavinking]

Here's an example of how you might use it, but it's much more general than this.

[gavinking]

Currently the API for this looks like:

@Formula(value = "credit * rate",
	overrides = @DialectOverride(dialect = H2Dialect.class, value = "rate * credit") )

I guess an alternative way to do it, that has less impact on the existing annotations, would be to write:

@Formula(value = "credit * rate")
@DialectOverride(annotation = Formula.class, dialect = H2Dialect.class, value = "rate * credit")

I'm unclear on which option is "better". I guess they're pretty equivalent.

[beikov]

Looks ok to me, but let's discuss the design first in #4528

[gavinking]

Superseded by #4607.