Revert "Revert "Reorder MLIRContext location in BuiltinAttributes.h""

This reverts commit 511dd4f4 along with
a couple fixes.

Original message:
Now the context is the first, rather than the last input.

This better matches the rest of the infrastructure and makes
it easier to move these types to being declaratively specified.

Phabricator: https://reviews.llvm.org/D96111