This patch adds the necessary constraint classes that are be used
by IRDL to define Operation, Type, and Attribute verifiers.
A constraint is a class inheriting the `irdl::Constraint` class,
which may call other constraints that are indexed by `unsigned`.
A constraint represent an invariant over an Attribute.
The `ConstraintVerifier` class group these constraints together,
and make sure that a constraint can only identify a single
attribute. So, once a constraint is used to check the
satisfiability of an `Attribute`, the `Attribute` will be
memorized for this constraint. This ensure that in IRDL, a
single `!irdl.attribute` value only correspond to a single
`Attribute`.
Depends on D144693
Reviewed By: Mogball
Differential Revision: https://reviews.llvm.org/D145733
3ffd13b183