feat: DH-19292 Add ui.table selection event

[mattrunyon]

Tested with this code (mostly to test Ctrl+a with a large table doesn't hang)

I would not recommend sorting this table as it almost instantly OOM my 20GB DH instance

from deephaven import ui, empty_table

t = ui.table(
    empty_table(1_000_000_000).update_view(["I=ii", "J=I*2"]),
    on_selection_change=lambda d: print(d),
    always_fetch_columns="I"
)

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[mofojed]

Looks good - my only comment is if we should bother throwing if always_fetch_columns isn't provided as well.

[mofojed]

Maybe we should throw if on_selection_change is set and always_fetch_columns is not set. Right now it just returns empty data if you don't specify always_fetch_columns. Though I guess in theory that would still tell you want the size of the selection is, and maybe that's all the want to know?

[mattrunyon]

Ya I added it to the Python side. Throws immediately if not wrapped in a component. If in a component, it will propagate to the client as a render error so the user can see something in that case still.

Did spot a weird case where I ran working code followed by code that threw and the panel just disappeared. I'll investigate a bit more and file a ticket

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