refactor(editor): the self-test commands in a file per group instead of one file of 4200 lines

editormodeselftest.cpp keeps the dispatch, the list of the commands and the step; the groups go to
editormodeselftest{scene,sleepers,sweep,track,switch,join,signal,terrain,rails}.cpp, the sleeper commands (beams,
sharedzones, sleepersbg, beamsnear, sleepercheck) in a group of their own; the frame count and one_line shared through
editormodeselftest.h. The output of geomhash, sleepercheck, wings, space, guards, crossings and switches is the same on the
seven sceneries of the regression.

application/editormodeselftest.h

@@ -0,0 +1,33 @@
+/*
+This Source Code Form is subject to the
+terms of the Mozilla Public License, v.
+2.0. If a copy of the MPL was not
+distributed with this file, You can
+obtain one at
+http://mozilla.org/MPL/2.0/.
+*/
+
+#pragma once
+
+#include <algorithm>
+#include <cstddef>
+#include <string>
+
+// what the groups of the self-test commands share, each group in a file of its own
+namespace editor_selftest
+{
+
+// frames gone through the selftest, for the measurements of perf
+inline std::size_t &frames()
+{
+	static std::size_t count{0};
+	return count;
+}
+
+inline std::string one_line(std::string Text)
+{
+	std::replace(Text.begin(), Text.end(), '\n', ';');
+	return Text;
+}
+
+} // namespace editor_selftest