si-menu: Improve and extend our examples

[kfenner]

The current menu example we're using in our docs is not great. E.g. the example is missing to show how to open a menu via a three-dots button as many apps just use the content action bar instead (NOT GOOD).

1. Improve the example as follows:
   

   So we should only use a relatively small menu to make these examples realistic and working well in the limited space of the previewer.

2. Therefore, we should add a second separate example file showing the full menu with all the options. Maybe call it "full-options" or something. Maybe there we could directly inline the menu so it is always open and the user doesn't need to click on a button first. Could also simplify the VRTs. See e.g. Carbon also just having it inlined: https://carbondesignsystem.com/components/menu/usage/