Align demos with the structure of AddonStarter

[javier-godoy]

Describe the bug

#125 did not pass the tests in AddonsDemo

Expected behavior

LayoutTest must pass

Minimal reproducible example

https://github.com/FlowingCode/AppLayoutAddon

Add-on Version

6.0.1-SNAPSHOT

Vaadin Version

24.5.0

Additional information

See https://github.com/FlowingCode/AddonsDemo/blob/vaadin24/src/test/java/com/flowingcode/vaadin/addons/LayoutTest.java

[javier-godoy]

I did reset the master branch and moved the code of #125 to new-demo

[mlopezFC]

@javier-godoy is this still a thing?