keep_classnames and keep_fnames missing from TypeScript definition file

[StephenWeatherford]

• Operating System: N/A
• Node Version: N/A
• NPM Version: N/A
• webpack Version: 4.28.1
• terser-webpack-plugin Version: 1.2.1

Expected Behavior

No typescript warnings in webpack.config.js file

keep_classnames and keep_fnames should be defined in typescript definition file but are not:

export interface MinifyOptions {
spidermonkey?: boolean;
outSourceMap?: string;
sourceRoot?: string;
inSourceMap?: string;
fromString?: boolean;
warnings?: boolean;
mangle?: boolean | MangleOptions;
output?: OutputOptions;
compress?: boolean | CompressOptions;
nameCache?: {};
}

Actual Behavior

Typescript squigglies:

Code

    optimization: {
        minimizer: [
            new TerserPlugin({
                terserOptions: {
                    // https://github.com/webpack-contrib/terser-webpack-plugin/

                    // Without this, parseError() will not recognize user cancelled errors.  Also makes debugging easier in production.
                    keep_classnames: true
                }
            }),
        ],
    },```

### How Do We Reproduce?

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[alexander-akait]

Out of scope plugin, all types should be in DefinitelyTyped repo, please create issue in DefinitelyTyped repo