Spring Transform upper keys to coroutines context fix #23859

@sdeleuze , I think it would be better if keys which are coroutinesContext will be transform in upper keys, but not only as keys to ReactorContext. ReactorContext is uncomfortable to use.

See #23859

Comment From: sdeleuze

Hi and sorry for the long delay for reviewing this PR. Unless I miss something, Reactor / Coroutines context interoperability is expected to be performed at https://github.com/Kotlin/kotlinx.coroutines/ level (more specifically here). If something does not behaves as expected, please report the issue with a reproducer in their issue tracker.

If the related issue is Spring specific, please comment and provide a reproducer (JUnit test if possible, otherwise application).