Custom monitors can be added/removed/checked using `Performance.add_custom_monitor`/`Performance.remove_custom_monitor`/`Performance.has_custom_monitor`
The value can be viewed in the `Monitor` tab of Debugger.
Text before `/` is used to categorize the custom monitor.
`EditorPerformanceProfiler` class is created to separate logic from `ScriptEditorDebugger`
User can click on the graph of monitors to read the value at that point.
Graph includes intermediate base lines.
