function normalizeSeverityToNumber(severity) {
	if ([2, "2", "error"].includes(severity)) {
		return 2;
	}
	if ([1, "1", "warn"].includes(severity)) {
		return 1;
	}
	if ([0, "0", "off"].includes(severity)) {
		return 0;
	}
	throw new Error(`Invalid severity value: ${severity}`);
}
Convert severity value of different types to a number.
@param {string|number} severity severity value
@throws error if severity is invalid
@returns {number} severity number