fs: support VFS-based named event group

[fxysunshine]

Summary

This extension for the event group, to establish a connection between named event groups and a task. The task may reference the event group associated with a VFS-based name. Then the event group can be used in subsequent calls to nxevent_wait() or nxevent_post().

This is an internal OS interface and should not be used by applications.

Impact

none, add OS interface

Testing

vela

[fxysunshine]

CI failed. Waiting for a dependent patch .