Make @types/next Document generic for defining custom props. (#28429)

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If changing an existing definition:
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I'm not familiar with writing these kind of testing code, so I didn't update that. Give me some guidance if necessary. Thanks.

types/next/document.d.ts

@@ -57,6 +57,6 @@ export interface NextScriptProps {
 export class Head extends React.Component<HeadProps> {}
 export class Main extends React.Component {}
 export class NextScript extends React.Component<NextScriptProps> {}
-export default class extends React.Component<DocumentProps> {
+export default class Document<TProps = {}> extends React.Component<TProps & DocumentProps> {
     static getInitialProps(ctx: NextDocumentContext): Promise<DocumentProps> | DocumentProps;
 }