Allow prefix class types as arguments for transient-scope

[aurtzy]

Would it be a good idea to allow prefix classes/types as arguments in addition to a specific command (or list of)? My concern is that it is not straightforward to extend if I want other prefixes (not necessarily defined in the package) to be accepted as well.

For example, I have defined a prefix class with a custom transient-init-scope method. The expectation is that any prefixes of this class/type will use the format from this transient-init-scope. It thus seems desirable to allow transient-scope to return a non-nil value if a prefix matches that type.

Alternatives for this use case that don't require changing the current implementation:

• Define a list variable for "compatible prefixes" that can be added to by the user or external packages.
• It might also work to add some hook/method-with-qualifier to the prefix class that automatically does this.

[tarsius]

I considered that case but decided against implementing it because it would complicate the documentation and likely be rarely used. I've implemented (but not tested) it now, see the 334 branch.

It would help me to decide whether this should be merged if you could implement your prefix commands without using this feature and then add an additional commit that demonstrates how that could be simplified by using this feature.