SPA_MEMBER is misleading, all we're doing here is pointer+offset and a
type-casting the result. Rename to SPA_PTROFF which is more expressive (and
has the same number of characters so we don't need to re-indent).
Make a new complete event and use it instead of the start event
Use the start event at the start of the cycle
Make the profiler also log incomplete graph cycles
Add Profiler object and fields.
Add profiler extension API. It notifies Profiler objects with
real-time performance data.
Add module that implements the profiler extension.
Add pw-profiler tool that binds to the profiler API and dumps the
data into a log file, gnuplot files, a html page and a script to
generate svg graphs. This is almost the same as what JACK2
JackEngineProfiling does.
