Create a migration that fixes CountedMap counts.

[ruseinov]

A continuation of #13214.

Basically anybody who's been using set on a CountedMap before the aforementioned PR was merged needs to call initialize_counter on that map.

[kianenigma]

None of our runtimes had an issue regarding this. So while I agree that we need to communicate this to the outer world in case they did use the wrong function, I don't think having an issue here is the right way.

This issue should be closed by someone writing a recalculate method for counted maps that re-generates the counter.

[ruseinov]

@kianenigma afaik recalculate already exists, will confirm and close

[ruseinov]

Yep, here it is: initialize_counter. I think we can close this.

[Polkadot-Forum]

This issue has been mentioned on Polkadot Forum. There might be relevant details there:

https://forum.polkadot.network/t/polkadot-release-analysis-v0-9-38/2122/1