This allows instruments to record a diagnostic and have it land as an
object in a GListModel of diagnostics available to the API consumer.
Such items may be used by recording UI to display issues with the recording
to the user.
The goal here is to have a fairly small exposed API surface for profiling
similar to libsysprof-analyze where implementation details are hidden.
SysprofProfiler - Where you setup your recording
SysprofInstrument - What you add to a profiler to extract data
SysprofRecording - Represents an active recording w/ instruments
