Improve engine startup/shutdown benchmarks

- Add contexts to give a better sense of benchmarked areas.
- Add missing benchmarks and adjust some begin/end points.
- Clean up names.
- Improve Android's internal benchmarks in a similar manner.

Co-authored-by: Fredia Huya-Kouadio <fhuya@meta.com>

editor/editor_help.h

@@ -187,6 +187,7 @@ class EditorHelp : public VBoxContainer {
 	String _fix_constant(const String &p_constant) const;
 	void _toggle_scripts_pressed();
 
+	static int doc_generation_count;
 	static String doc_version_hash;
 	static Thread worker_thread;