…ython#124776)"This reverts commit843d28f.

…d" (#124776)" (#125513)

…events with "switched" (python#124776)" (python#125513)"This reverts commitd3c82b9.

…4776)Users want to know when the current context switches to a differentcontext object.  Right now this happens when and only when a contextis entered or exited, so the enter and exit events are synonymous with"switched".  However, if the changes proposed forpythongh-99633 areimplemented, the current context will also switch for reasons otherthan context enter or exit.  Since users actually care about contextswitches and not enter or exit, replace the enter and exit events witha single switched event.The former exit event was emitted just before exiting the context.The new switched event is emitted after the context is exited to matchthe semantics users expect of an event with a past-tense name.  Ifusers need the ability to clean up before the switch takes effect,another event type can be added in the future.  It is not added herebecause YAGNI.I skipped 0 in the enum as a matter of practice.  Skipping 0 makes iteasier to troubleshoot when code forgets to set zeroed memory, and italigns with best practices for other tools (e.g.,https://protobuf.dev/programming-guides/dos-donts/#unspecified-enum).