Revert "ValidationProcessor: calculate ref resolving input _before_ validation"

This reverts commit 058294f6f6720e0e5d7732d47ad69cf92c742405.

It has provoked a huge degradation in performance for no reason that I can
see...
ValidationProcessor: fix $ref bug another way

Instead of passing the input as an argument to process{Array,Object}(), pass the
data calculated in the full context.

But the performance is still horrid, and I cannot figure out why.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
Create a new ValidationContext class

All the chain from ref resolving up to format keyword attachment does not care
about the full instance, only its type: create a dedicated (and more easily
cacheable) structure for this.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>