Move stubs from ./stubs to ./shared/Stubs

Gathers all shared test code in single place.

tests/unit/shared/Stubs/SelectedScriptStub.ts

@@ -0,0 +1,8 @@
+import { SelectedScript } from '@/application/Context/State/Selection/SelectedScript';
+import { ScriptStub } from './ScriptStub';
+
+export class SelectedScriptStub extends SelectedScript {
+  constructor(id: string, revert = false) {
+    super(new ScriptStub(id), revert);
+  }
+}