src/vs/workbench/services/editor/browser/editorService.ts/EditorService/isOpened
class EditorService:	isOpened(editor: IResourceEditorInputIdentifier): boolean {
		return this.editorsObserver.hasEditor({
			resource: this.uriIdentityService.asCanonicalUri(editor.resource),
			typeId: editor.typeId,
			editorId: editor.editorId
		});
	}