Add deprecated value field for backward source compatibility with http4s CaseInsensitiveString

[bplommer]

Related to http4s/http4s#5344

[rossabaker]

This could aid people upgrading from http4s-0.21, but when that's done, this cruft is forever. Or at least until case-insensitive-2, which I hope doesn't need to happen. 🤔

[rossabaker]

It's similar to http4s/http4s#5344, but people who have found their way to this type have already changed code. (Still thinking out loud).

[bplommer]

This could aid people upgrading from http4s-0.21, but when that's done, this cruft is forever.

True 😕 it could be added to http4s as an extension instead along with .ci, though that wouldn't catch all uses.

[bplommer]

but people who have found their way to this type have already changed code.

Not necessarily - various things return CIString that previously returned CaseInsensitiveString, and once that PR is merged the aliases will automatically forward them to this type.

[rossabaker]

That's a good point.

[rossabaker]

Let's do it. Deprecation handholding is nice.