<!-- Click "Preview" for a more readable version --

Please read and follow the instructions before submitting an issue:

- Read all our documentation, especially the [README](https://github.com/axios/axios/blob/master/README.md). It may contain information that helps you solve your issue.
- Ensure your issue isn't already [reported](https://github.com/axios/axios/issues?utf8=%E2%9C%93&q=is%3Aissue).
- If you aren't sure that the issue is caused by Axios or you just need help, please use [Stack Overflow](https://stackoverflow.com/questions/tagged/axios) or [our chat](https://gitter.im/mzabriskie/axios).
- If you're reporting a bug, ensure it isn't already fixed in the latest Axios version.
- Don't remove any title of the issue template, or it will be treated as invalid by the bot.

⚠️👆 Feel free to these instructions before submitting the issue 👆⚠️
-->

#### Describe the bug

I tried to use the function added in #4248 with TypeScript, but got the following error.

```
Property 'clear' does not exist on type 'AxiosInterceptorManager<AxiosRequestConfig<any>>
```

#### To Reproduce

Execution is possible, but type checking fails.

```ts
import axios from "axios";

axios.interceptors.request.clear()
```

#### Expected behavior

Successful type check

#### Environment
 - Axios 1.0.0
 - TypeScript 4.8.4

#### Additional context/Screenshots

index.d.ts

type AxiosHeaderValue = string | string[] | number | boolean | null;
type RawAxiosHeaders = Record<string, AxiosHeaderValue>;
type MethodsHeaders = {
  [Key in Method as Lowercase<Key>]: AxiosHeaders;
};
interface CommonHeaders  {
  common: AxiosHeaders;
}
type AxiosHeaderMatcher = (this: AxiosHeaders, value: string, name: string, headers: RawAxiosHeaders) => boolean;
type AxiosHeaderSetter = (value: AxiosHeaderValue, rewrite?: boolean | AxiosHeaderMatcher) => AxiosHeaders;
type AxiosHeaderGetter = ((parser?: RegExp) => RegExpExecArray | null) |
    ((matcher?: AxiosHeaderMatcher) => AxiosHeaderValue);
type AxiosHeaderTester = (matcher?: AxiosHeaderMatcher) => boolean;
export class AxiosHeaders {
  constructor(
      headers?: RawAxiosHeaders | AxiosHeaders,
      defaultHeaders?: RawAxiosHeaders | AxiosHeaders
  );
  set(headerName?: string, value?: AxiosHeaderValue, rewrite?: boolean | AxiosHeaderMatcher): AxiosHeaders;
  set(headers?: RawAxiosHeaders | AxiosHeaders, rewrite?: boolean): AxiosHeaders;
  get(headerName: string, parser: RegExp): RegExpExecArray | null;
  get(headerName: string, matcher?: true | AxiosHeaderMatcher): AxiosHeaderValue;
  has(header: string, matcher?: true | AxiosHeaderMatcher): boolean;
  delete(header: string | string[], matcher?: AxiosHeaderMatcher): boolean;
  clear(): boolean;
  normalize(format: boolean): AxiosHeaders;
  toJSON(): RawAxiosHeaders;
  static from(thing?: AxiosHeaders | RawAxiosHeaders | string): AxiosHeaders;
  static accessor(header: string | string[]): AxiosHeaders;
  setContentType: AxiosHeaderSetter;
  getContentType: AxiosHeaderGetter;
  hasContentType: AxiosHeaderTester;
  setContentLength: AxiosHeaderSetter;
  getContentLength: AxiosHeaderGetter;
  hasContentLength: AxiosHeaderTester;
  setAccept: AxiosHeaderSetter;
  getAccept: AxiosHeaderGetter;
  hasAccept: AxiosHeaderTester;
  setUserAgent: AxiosHeaderSetter;
  getUserAgent: AxiosHeaderGetter;
  hasUserAgent: AxiosHeaderTester;
  setContentEncoding: Axios