Refactor Keyboard Logic

[mastapegs]

This logic is pretty messy. We could refactor it in several ways:

• Use Array.prototype.map instead of .forEach
• Refactor IIFE

js-marathon-web-audio-api/components/Keyboard/Keyboard.tsx

Lines 23 to 32 in b1b040a

	(() => {
	const keys: Array<ReactNode> = [];
	noteFreq.forEach((octaveTable, octave) => {
	const keyList = Object.entries(octaveTable);
	keyList.forEach((key) => {
	keys.push(<Key note={key[0]} octave={octave} freq={key[1]} />);
	});
	});
	return keys;
	})()}