fix: 🐛 issue with "Untitled Slide" already exists in builder

When adding new slides via withSlide() in DeckBuilder and do not provide
names for these slides, it uses "Untitled Slide" by default. The problem
is that when you adding more than one such slide, it throws an error
that slide already exists. This commit fixes it by introducing a random
suffix to "Untitled Slide" name.

src/main/kittik-slide/spec/Slide.spec.ts

@@ -78,6 +78,13 @@ const SERIALIZED_SLIDE_DECLARATION: SlideDeclaration = {
 };
 
 describe('slide', () => {
+  it('should properly generate a unique name by default', () => {
+    expect.hasAssertions();
+
+    const slide = new Slide();
+    expect((/Untitled Slide #.{7}/u).test(slide.name)).toBe(true);
+  });
+
   it('should properly throw an error if shape type is unknown', () => {
     expect.hasAssertions();
 

src/main/kittik-slide/src/slide/Slide.ts

@@ -20,7 +20,7 @@ export { SlideDeclaration } from './SlideDeclaration';
 
 export class Slide {
   public canvas: Canvas = Canvas.create();
-  public name = 'Untitled Slide';
+  public name = `Untitled Slide #${Math.random().toString(36).slice(2)}`;
   public readonly shapes: Map<string, ShapeRenderable> = new Map<string, ShapeRenderable>();
   public readonly animations: Map<string, Animationable> = new Map<string, Animationable>();
   public readonly order: OrderDeclaration[] = [];