Bug report

Hi, the type of Rules seems to break since the PR https://github.com/webpack-contrib/terser-webpack-plugin/pull/561/files#diff-093ad82a25aee498b11febf1cdcb6546e4d223ffcb49ed69cc275ac27ce0ccceR138 cc: @alexander-akait

The type of Rules was:

type Rule = RegExp | string;
type Rules = Rule[] | Rule; // => (RegExp | string)[] | RegExp | string

But now, it's:

type Rules = string | string[] | RegExp | RegExp[];

This breaking change makes it not valid any more to declare an array containing both strings and RegExp's to options.test/include/exclude, which looks unexpected. Would you take a look? Thanks.

Actual Behavior

Expected Behavior

How Do We Reproduce?

Please paste the results of npx webpack-cli info here, and mention other relevant information