ref: Convert SentryWatchdogTerminationScopeObserver to Swift

[github-actions]

Note

The pull request "ref: Convert SentryWatchdogTerminationScopeObserver to Swift" was created by @noahsmartin but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

Pulled out this small swift conversion from my larger dependency container PR to make it easier to review

#skip-changelog

[linear]

COCOA-816