Log Events to EventPipe on Linux (dotnet/coreclr#11433)

Log Events to EventPipe on Linux (dotnet/coreclr#11433)

* Implement the EventPipe object model for providers and events.

* Plumb Runtime Events into EventPipe (dotnet/coreclr#11145)

Plumb runtime ETW events into the EventPipe.

* Fix bug where all events except for SampleProfiler events were never enabled.

* Plumb EventPipeEventInstance through the EventPipe.

* Implement EventPipeFile and FastSerializer.

* Write event contents to the EventPipeFile.

* Only build EventPipe on Linux.

* Conditionally add a sentinel value marking event end.

* Send SampleProfiler events to the EventPipeFile.

* Fix provider ID printing to JSON file.

* Write the start date/time, timestamp, and clock frequency into the trace file.

* Support unloading of EventPipeProviders.

* Handle failure cases when we can't walk the stack or are shutting down.

* Fix a bug where we pass a null src pointer to memcpy.

Commit migrated from https://github.com/dotnet/coreclr/commit/72ac46450bec8ea88ed023d9c1faf5a04556c834