Currently, selecting an event with children (e.g. vkCmdExecuteCommands)
in the event browser will cause the API inspector window to show the
final child event, rather than the event itself. This behaviour makes
sense everywhere else: selecting an event with children shows the state
after all children have completed.
However, for the API inspector, we want to be able see API calls for
the parent event when it is selected rather than those of its last
child, particularly in the case of vkCmdExecuteCommands which may have
other API calls leading up to it.
To allow this, distinguish between the "current event" and "selected
event". For an event with children, the former refers to the last
child, while the latter refers to the event itself. ILogViewerForm now
has two separate event callbacks for when either one changes.
The API inspector now makes use of the selected event, while everything
else continues to use the current event.