Use KnownProps to ignore index signature

[atomiks]

Fixes #134

This ignores [key: string]: any from Props interface, allowing autocomplete and type validation to actually work in this package. (It works fine in tippy.js core [autocomplete & types validation works] but not when extended here, idk why I'm not good with TS)

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Then we need to add back in the index signature for each of the extended interfaces so plugin props don't error (without needing to make your own type).

To make your own type for plugin props like followCursor which don't exist on Props, you need to make your own function type, like this, I think:

import Tippy, {TippyProps} from '@tippy.js/react';
import {followCursor, FollowCursorProps} from 'tippy.js';

const TippyExtended: React.FC<TippyProps & FollowCursorProps> = ({
 plugins,
 ...props
}) => <Tippy plugins={[followCursor, ...(plugins || [])]} {...props} />;

BUT since we're adding [key: string]: any to each of the extended interfaces, you don't need it just like in tippy.js - you just won't get autocompletion & type validation. So it's backwards-compatible with 3.0.0 and 3.0.1.

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TL;DR

• Extending an interface with [key: string]: any breaks autocomplete & type validation for all the known/declared types, so we need to only extend the KnownProps version of it
• We need to add back [key: string]: any to the extended interfaces to prevent unknown props (e.g. for plugins) from erroring. The user can create strict types for plugin props if they wish to. If they pass an unknown prop, there's a runtime DEV warning telling them that, instread of compile time TS warning (for JS users).
• This needs to be done for all TippyProps, TippySingletonProps, and UseSingletonProps interfaces.