Make sure types.Type instances are not mutated

[sklam]

it's because the type instance was mutated directly and the name of the type would not reflect this. Am happy to merge this patch as is, but for the future, perhaps it'd make sense to create a task for making types immutable to prevent this sort of accident from reoccurring?

Originally posted by @stuartarchibald in #7610 (review)

Todos:

• Use @property for attribute of Type instances.

[ehsantn]

This has bitten us quite a few times too :) Very hard to debug.

[MiloniAtal]

The Type Class already has @Property for attributes. To fix this do we need to check all the subclasses and see if they have immutable attributes i.e using the @Property decorator? Or is there anything else that needs to be done?