Incorporate new Virtual Threads JFR events into JFR viewer

[thurka]

JEP 444: Virtual Threads adds several new events JFR:

• jdk.VirtualThreadStart and jdk.VirtualThreadEnd indicate virtual thread start and end. These events are disabled by default.
• jdk.VirtualThreadPinned indicates that a virtual thread was parked while pinned, i.e., without releasing its platform thread (see above). This event is enabled by default, with a threshold of 20ms.
• jdk.VirtualThreadSubmitFailed indicates that starting or unparking a virtual thread failed, probably due to a resource issue. This event is enabled by default.

It would be great if this new JFR events can be used to provide info about Virtual threads in JFR viewer.