libsysprof-profile: add scaffolding for base objects

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

src/libsysprof-profile/sysprof-instrument-private.h

@@ -0,0 +1,39 @@
+/* sysprof-instrument-private.h
+ *
+ * Copyright 2023 Christian Hergert <chergert@redhat.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include "sysprof-instrument.h"
+
+G_BEGIN_DECLS
+
+#define SYSPROF_INSTRUMENT_GET_CLASS(obj) G_TYPE_INSTANCE_GET_CLASS(obj, SYSPROF_TYPE_INSTRUMENT, SysprofInstrumentClass)
+
+struct _SysprofInstrument
+{
+  GObject parent;
+};
+
+struct _SysprofInstrumentClass
+{
+  GObjectClass parent_class;
+};
+
+G_END_DECLS