Add more standardized menu for dropdown

[inooid]

Description

Currently the dropdown components (and sub components) make it possible to render anything within the "popped out" box, but this gives us consumers a lot of freedom. I would like to see some more guidance in how to render these dropdown lists.

How about a DropdownList or DropdownMenu component that is just a styled ul and li list?

Requirements

• Don't narrow down the API of the dropdown component itself, people should still be allowed to render things above or below the list.
• Standardise the way we create context menus

Design/Examples

Currently within the Lightspeed products, we've seen some context menus being used within the sidebar:

But also in our some other places:

Both of these designs already show and proof that the implementations are going all over the place, while they're pretty similar.

[tombertrand]

Can only think of these 2 for now, perhaps scope creep and remove that dotted like when a button is focused :creeper:

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