Better ordering infrastructure for lambda-based customizers

[snicoll]

Adding a default order for the customizer makes sure that we have a deterministic and more sensible default (0). The problem is that it trumps any attempt to use @Order and it's not super obvious.

It took me a bit to figure out what was going with this test.

If we want to set an order (which is why we did this in the first place), we can't nicely write a lambda.

[snicoll]

@philwebb suggested to use a custom OrderComparator or to try to set @Ordered(0) on the customizer interface