allowableValues doesn't work with array type

[liuxh0]

When I define an array-typed option with allowableValues, the validation doesn't seem to work properly.

Semantically I think this should be interpreted that this option accepts multiple values and each of the values should be allowable.

Currently, the validity is checked by this method:

imperative/packages/cmd/src/syntax/SyntaxValidator.ts

Lines 543 to 553 in ce314e1

	private checkIfAllowable(allowable: ICommandOptionAllowableValues, input: string): boolean {
	let matchFound: boolean = false;
	for (const value of allowable.values) {
	const flags = allowable.caseSensitive ? "g" : "ig";
	if (new RegExp(value, flags).test(input)) {
	matchFound = true;
	break;
	}
	}
	return matchFound;
	}

If the option is of type array, input is also of type array. Although the parameter of RegExp.test() should be of type string, it will somehow first convert other types to string and then perform regular expression match.

I want to extend the support for array. I offer to create a PR if this concept is okay.