Introduce CRTP TypeBase class to simplify type construction and validation.

This impl class currently provides the following:
* auto definition of the 'ImplType = StorageClass'
* get/getChecked wrappers around TypeUniquer
* 'verifyConstructionInvariants' hook
   - This hook verifies that the arguments passed into get/getChecked are valid
     to construct a type instance with.

With this, all non-generic type uniquing has been moved out of MLIRContext.cpp

PiperOrigin-RevId: 227871108