feat: allow frontend code in events

[mariobuikhuizen]

Making the following possible:

import ipyvuetify as v

activator = v.Sheet(style_="width: 500px; height: 500px", elevation=8)
activator.on_event("contextmenu.prevent", "menu.on.click")

v.Sheet(children=[
    v.Menu(
        v_slots=[
            {
                "name": "activator",
                "variable": "menu",
                "children": [activator],
            }
        ],
        absolute=True,
        children=[
            v.Btn(children=["hi"])
        ],
        
    ),
])

One thing I noticed though, is that we need an extra right-click to show the menu on a different spot. So it might not be useful for the original envisioned use-case.

[maartenbreddels]

Nice!
Any idea why this extra click is needed, is that an issue that needs solving?

I guess we could also do a UI test for this PR right? For instance a context menu?

[maartenbreddels]

Slightly unrelated but I think this code (81-95) is very hard to read, or does not work. The register_callback call with remove=True is a no-op or maybe it gives an exception?
Would make me feel more comfortable is we had a test for this.

[mariobuikhuizen]

Any idea why this extra click is needed, is that an issue that needs solving?

It's just how Vuetify menu works. Click out-side first closes the menu, the next click opens the menu on the new position. This is fine for menu, but as a context menu this is a bit unexpected.

[maartenbreddels]

Right, that means for solara, we probably need a custom template anyway.
I found this example https://codesandbox.io/s/vuetify-context-menu-opened-multiple-times-idstb?file=/src/main.js which seems impossible to do without a vue template.
cc @iisakkirotko