This allows grouping marks together so that the UI can present marks within
the same group in the same visualizer row.
The goal here is that our perf stream with drm data will have "drm" or some
similar group name (resulting in one row). mutter/cogl/gnome-shell will
use the thread-id as the group name (or something else that is useful) so
their events are grouped together. gdk-wayland might have it's own group
name as well.
The end result is that we can get a mark row for each series of related
data.
The goal here is to have an API that allows us to record things like
frame timing data. We might iterate on this API a bit, but this gets us
started.
A SpCaptureMark with a zero duration should be treated like an epoch mark
once a visualizer is created. SpCaptureMark with a non-zero duration should
be treated like a begin/end of operation. This may be useful in generating
something like a flame graph.
This allows external tooling to write capture files that Sysprof can open.
Ideally, this will get used by GJS in the near future to implement profiler
output for Sysprof.
The lib/ directory was getting a bit out of hand, so this tries
to organize things a bit so it is easier going forward to locate
the code people want to patch.
