.NET Profiling for ASP.NET Core

Follow up from:

* https://github.com/getsentry/sentry-dotnet/issues/2315
* https://github.com/getsentry/sentry-dotnet/issues/1955

- [ ] collect `Microsoft-Windows-DotNETRuntime` rundown provider (loaded libs, etc) in a separate session and merge with actual samples later during processing, if possible (merging nettrace files, or having a custom provider for TraceLog).
- [ ] Or maybe we don't even need to collect these because we're in the same process? can we hack our way around and get the libraries from the current process instead? Probably not so easy because it also somehow stack walking if I'm not mistaken.
- [ ] We'll use GlobalMode to set the behavior: all threads in process (global Mode) or only activity/request (server mode)
- [ ] Consider capturing only the current "activity", i.e. not all threads but only what belongs to the transaction.

- See also https://studylib.net/doc/6851938/eventsource-activity-support
- possible blocker https://github.com/microsoft/perfview/issues/2122