COM-310: Refactor theming of MenuItem

[juliawegmayr]

[johnnyomair]

@juliawegmayr please merge the feature branch and resolve conflicts, thanks!

[jamesricky]

@juliawegmayr the error in the pipeline is caused by a similar problem, as I fixed here: #1642

Since slotProps was added to MenuItemProps and MenuCollapsibleItemProps defines it's own slotProps and extends MenuItemProps it doesn't know which slotProps to use.

This can be fixed by extending MenuCollapsibleItemProps from Omit<MenuItemProps, "slopProps"> instead of MenuItemProps.

But to continue to allow overriding the slotProps of MenuItem inside MenuCollapsibleItem, the MenuItem needs to be a slot so slotProps can be passed into it.