[Feature Request] Trace callstacks include native frames

The GC team would love to see native callstacks for their events to better understand GC performance. This could either come via EventPipe support for native stacks or gathering the traces with a different tool such as PerfCollect. This is in the same set of requests as the [context switch request](https://github.com/dotnet/diagnostics/issues/463) and the [trigger request](https://github.com/dotnet/diagnostics/issues/464) so the goal is to have all of these capabilities in the same trace so they can be used together.

@Maoni0 @sywhang @josalem