Better distinguish override completions in tooltip

[jakebailey]

Right now, completions for function overrides look like:

I don't think that it's very clear that selecting this completion will actually fill out a full function rather than just completing the name for you (which is what jedi does with the same exact hint name). I think it'd be better to include some extra text in the tooltip, like:

To better show what the completion actually does.

[jakebailey]

FWIW, the above is just:

private CompletionItem ToOverrideCompletionItem(IOverloadResult o, ClassDefinition cd, string indent) {
    return new CompletionItem {
        label = o.Name + " (override)",
        insertText = MakeOverrideCompletionString(indent, o, cd.Name),
        kind = CompletionItemKind.Method
    };
}