[mlir] Make some functions public to use custom TypeIDs

Currently, it is only possible to register an operation or a type
when the TypeID is defined at compile time. Same with InterfaceMaps
which can only be defined with compile-time defined interfaces.

With those changes, it is now possible to register types/operations
with custom TypeIDs. This is necessary to define new operations/types
at runtime.

Differential Revision: https://reviews.llvm.org/D99084