File / Folder Names that contain parentheses do not resolve

## 🐛 Bug Report

### Prerequisites

- [x] I'm using the latest version of Docusaurus.
- [X] I have tried the `npm run clear` or `yarn clear` command.
- [X] I have tried `rm -rf node_modules yarn.lock package-lock.json` and re-installing packages.
- [X] I have tried creating a repro with https://new.docusaurus.io
- [X] I have read the console error message carefully (if applicable)

### Description

Parentheses are not allowed in a file / folder name. When a file has parentheses the file still shows up in the sidebar but when clicked shows "page not found".

## Steps to reproduce

1. Create a file or folder that has `(` or `)` in the name.
2. Go to that file in the sidebar.

CodeSandbox doesn't allow the special character... but stackblitz does. Demo:

https://stackblitz.com/edit/github-eranrw?file=docs/another(1).md

## Expected behavior

I would expect it to be able to resolve the special character.

## Actual behavior

The page did not resolve and seems to be considered a broken markdown link.