refactor(workbench/dialog): consolidate API for closing a dialog

BREAKING CHANGE: The method `closeWithError` has been removed from the `WorkbenchDialog` handle. Instead pass an `Error` object to the `close` method.

### The following snippets illustrate how a migration could look like:

#### Before migration

```ts
import {WorkbenchDialog} from '@scion/workbench';

inject(WorkbenchDialog).closeWithError('some error');
```

#### After migration

```ts
import {WorkbenchDialog} from '@scion/workbench';

inject(WorkbenchDialog).close(new Error('some error'));
```

apps/workbench-testing-app/src/app/dialog-page/dialog-page.component.ts

@@ -79,12 +79,8 @@ export class DialogPageComponent {
   }
 
   public onClose(): void {
-    if (this.form.controls.closeWithError.value) {
-      this.dialog.closeWithError(this.form.controls.result.value);
-    }
-    else {
-      this.dialog.close(this.form.controls.result.value);
-    }
+    const result = this.form.controls.closeWithError.value ? new Error(this.form.controls.result.value) : this.form.controls.result.value;
+    this.dialog.close(result);
   }
 
   private installPropertyUpdater(): void {

projects/scion/workbench/src/lib/dialog/workbench-dialog.ts

@@ -54,14 +54,9 @@ export abstract class WorkbenchDialog<R = unknown> {
   public abstract cssClass: string | string[];
 
   /**
-   * Closes the dialog. Optionally, pass a result to the dialog opener.
+   * Closes the dialog. Optionally, pass a result or an error to the dialog opener.
    */
-  public abstract close(result?: R): void;
-
-  /**
-   * Closes the dialog returning the given error to the dialog opener.
-   */
-  public abstract closeWithError(error: Error | string): void;
+  public abstract close(result?: R | Error): void;
 }
 
 /**

projects/scion/workbench/src/lib/dialog/ɵworkbench-dialog.ts

@@ -48,9 +48,9 @@ export class ɵWorkbenchDialog<R = unknown> implements WorkbenchDialog<R>, Block
   private _blink$ = new Subject<void>();
 
   /**
-   * Contains the result to be passed to the dialog opener.
+   * Result (or error) to be passed to the dialog opener.
    */
-  private _result: R | ɵDialogErrorResult | undefined;
+  private _result: R | Error | undefined;
   private _componentRef: ComponentRef<WorkbenchDialogComponent> | undefined;
   private _cssClass: string;
 
@@ -108,28 +108,17 @@ export class ɵWorkbenchDialog<R = unknown> implements WorkbenchDialog<R>, Block
     // Wait for the dialog to close, resolving to its result or rejecting if closed with an error.
     return new Promise<R | undefined>((resolve, reject) => {
       this._destroyRef.onDestroy(() => {
-        if (this._result instanceof ɵDialogErrorResult) {
-          reject(this._result.error);
-        }
-        else {
-          resolve(this._result);
-        }
+        this._result instanceof Error ? reject(this._result) : resolve(this._result);
       });
     });
   }
 
   /** @inheritDoc */
-  public close(result?: R): void {
+  public close(result?: R | Error): void {
     this._result = result;
     this.destroy();
   }
 
-  /** @inheritDoc */
-  public closeWithError(error: Error | string): void {
-    this._result = new ɵDialogErrorResult(error);
-    this.destroy();
-  }
-
   /**
    * Inputs passed to the dialog.
    */
@@ -358,12 +347,3 @@ export class ɵWorkbenchDialog<R = unknown> implements WorkbenchDialog<R>, Block
     }
   }
 }
-
-/**
- * Wrapper to identify an erroneous result.
- */
-class ɵDialogErrorResult {
-
-  constructor(public error: string | Error) {
-  }
-}