observable for detecting if split view is active (#19394)

* observable for detecting if split view is active

* declare splitView manager on content detail workspace

* remove declaration as it was a double

Author: nielslyngsoe

src/Umbraco.Web.UI.Client/src/packages/core/workspace/controllers/workspace-split-view-manager.controller.ts

@@ -16,6 +16,7 @@ export class UmbWorkspaceSplitViewManager {
 		(a, b) => (a.index || 0) - (b.index || 0),
 	);
 	public readonly activeVariantsInfo = this.#activeVariantsInfo.asObservable();
+	public readonly splitViewActive = this.#activeVariantsInfo.asObservablePart((x) => x.length > 1);
 
 	private _routeBase?: string;
 	public getWorkspaceRoute(): string | undefined {