[BUG]Unable to use Exceljs (4.1.1) in IE11 using Angular 9

## 🐛 Bug Report

Invalid range in character set" error on IE11 if using excelJs.

Lib version:
package.json
------------------------

"@angular/animations": "~9.0.3",
"@angular/cdk": "^9.2.4",
"@angular/common": "~9.0.3",
"@angular/compiler": "~9.0.3",
"@angular/core": "~9.0.3",
"@angular/forms": "~9.0.3",
"exceljs": "^4.1.1",

Polyfills.ts
-------------

import 'core-js'
require('core-js/modules/es.promise');
require('core-js/modules/es.string.includes');
require('core-js/modules/es.object.assign');
require('core-js/modules/es.object.keys');
require('core-js/modules/es.symbol');
require('core-js/modules/es.symbol.async-iterator');
require('regenerator-runtime/runtime');
import 'regenerator-runtime/runtime';
import './unicode-regex-polyfill';

unicode-regex-polyfill.ts
---------------------------------------------

import rewritePattern from 'regexpu-core';
import { generateRegexpuOptions } from '@babel/helper-create-regexp-features-plugin/lib/util';
const { RegExp } = global;
try {
new RegExp('a', 'u');
} catch (err) {
// @ts-ignore
global.RegExp = function(pattern, flags) {
if (flags && flags.includes('u')) {
return new RegExp(
rewritePattern(
pattern,
flags,
generateRegexpuOptions({ flags, pattern })
)
);
}
return new RegExp(pattern, flags);
};
// @ts-ignore
global.RegExp.prototype = RegExp;
}