[TASK] Prepare ImmediateActionElementTest for ES6 modules

In ES6 mode Viewport.Topbar and ModuleMenu.App properties
cannot be overwritten (in order to be substituted with a call spy),
as they reference other JavaScript modules.
The properties of ES6 models are readonly ("frozen") and can
therefore not be overwritten in a test setup.

Therefore the test is adapted to overwrite the references
in Viewport and ModuleMenu instead.

Also a timeout is added as await import('TYPO3/CMS/Backend/ModuleMenu')
does not guarantee a loading order between modules in ES6, which
causes test asserts to be executed too early.

Releases: main
Resolves: #96396
Related #96323
Change-Id: I5c213b70e43c5e1256e91ffe0d9f12f96dbb6615
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72736


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Benjamin Franzke <bfr@qbus.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>