[release/6.0-rc1] Add event to RuntimeEventSource for AppContext switches (#57847)

[release/6.0-rc1] Add event to RuntimeEventSource for AppContext switches (#57847)

* Add event to RuntimeEventSource for AppContext switches

Fixes https://github.com/dotnet/runtime/issues/56142

* Respond to PR comments

* Add preliminary tests

* Respond to PR comments

* Add keyword

* Fix tests

* Remove AppContext EventSource support on browser

* forgot using

* Fix error reporting, add comments

* Respond to PR comments

* Refactor tests

* Fix case where s_switches is null

* Fix bug

* Print more info for test failure

* Typo

* Fix lab failure

* Respond to PR comments

* Respond to PR comments

* Typo

* Respond to PR comments

* Skip RuntimeEventSource tests on wasm and android (#57890)

* Skip RuntimeEventSource tests on wasm and android

* Skip tests without using issues.targets

* Disable test for mono

(cherry picked from commit 454ac571fe489ab818c7727f11eee71d521c4366)

Co-authored-by: Andy Gocke <angocke@microsoft.com>