libsysprof-profile: start on perf event stream

This is a bit different than how we did things previously, but the same
mechanics are involved. Instead of multiple CPU registered together, we'll
just use one-stream-per-cpu.

Partly because I intend to drop support for profiling a single process as
that doesn't really get used much nor does it seem to yield very good
results from perf.

src/libsysprof-profile/meson.build

@@ -12,6 +12,7 @@ libsysprof_profile_public_sources = [
 libsysprof_profile_private_sources = [
   'mapped-ring-buffer-source.c',
   'sysprof-controlfd-instrument.c',
+  'sysprof-perf-event-stream.c',
   'sysprof-podman.c',
   'sysprof-polkit.c',
 ]