function parseMappingArgument(globalStrings, processValue) {
	const globals = {};
	globalStrings.split(',').forEach(globalString => {
		let [key, value] = globalString.split('=');
		if (processValue) {
			const r = processValue(value, key);
			if (r !== undefined) {
				if (Array.isArray(r)) {
					[value, key] = r;
				} else {
					value = r;
				}
			}
		}
		globals[key] = value;
	});
	return globals;
}
Parses values of the form "$=jQuery,React=react" into key-value object pairs.