libsysprof-gtk: add xy layer to allow some code deduplication

We can also port ColumnLayer to use this.

src/libsysprof-gtk/sysprof-xy-layer-private.h

@@ -0,0 +1,52 @@
+/* sysprof-xy-layer-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-normalized-series.h"
+#include "sysprof-xy-layer.h"
+
+G_BEGIN_DECLS
+
+struct _SysprofXYLayer
+{
+  SysprofChartLayer        parent_instance;
+
+  GBindingGroup           *series_bindings;
+  SysprofXYSeries         *series;
+
+  SysprofAxis             *x_axis;
+  SysprofAxis             *y_axis;
+
+  SysprofNormalizedSeries *normal_x;
+  SysprofNormalizedSeries *normal_y;
+};
+
+struct _SysprofXYLayerClass
+{
+  SysprofChartLayerClass parent_instance;
+};
+
+void _sysprof_xy_layer_get_xy (SysprofXYLayer  *self,
+                               const float    **x_values,
+                               const float    **y_values,
+                               guint           *n_values);
+
+G_END_DECLS