[drivers][power] Add inspect to element runner

Optionally take an inspect node when constructing an
ElementRunner. The runner populates properties on the node for
element name, current level, and required level.

LeaseHelper also takes an inspect node optionally, since it uses
ElementRunner in its implementation.

Bug: 388858484

Change-Id: I7a507115c6c71c30f5a99b031c91c297a5354161
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1180098
Commit-Queue: Justin Mattson <jmatt@google.com>
Reviewed-by: Novin Changizi <novinc@google.com>