FRAME Storage remove_all API should have a key limit

[shawntabrizi]

Similar to the storage_kill api in child tries, the remove_all api on any maps should also have an optional key limit to enforce weight restrictions.

#8166

When calling remove_all, a user should also be able to include Option<u32>, which describes the maximum number of keys that can be removed at once.

At the end of the operation, you can return AllRemoved(u32) or SomeReamining(u32) with the number of items that were actually removed at the end of the operation.

Should reuse and rename KillChildStorageResult:

https://github.com/paritytech/substrate/blob/master/primitives/io/src/lib.rs#L89

[xlc]

#8742 should I close my one?

[shawntabrizi]

ah didnt see it. Yeah this is a bit more descriptive, and I will have someone work on it soon.