[api-documenter] Avoid putting markdown/text after an HTML tag

[markus-incisive]

Summary

Sometimes, the generated Markdown has a closing HTML tag followed by text, without any blank lines in-between. This can mess up some Markdown engines, including GitHub and VSCode.

Repro steps

Given the following .d.ts code

/**
 * Adds two numbers.
 * @param a - The first number.
 * @param b - The second number.
 * @returns The sum.
 *
 * @public
 */
export declare function add(a: number, b: number): number;

running

> api-extractor run
> api-documenter markdown

results in

## Parameters

<table><thead><tr><th>
  <!-- ... -->
</tbody></table>
**Returns:**

number

The sum.

Since **Returns:** follows immediately after an HTML tag, it is not rendered properly.

VSCode:

Details

This issue appears with pretty much any function with parameters. It can be fixed by adding a blank line.

Relevant issue: https://github.com/microsoft/vscode-markdown-tm-grammar/issues/85

Standard questions

Please answer these questions to help us investigate your issue more quickly:

Question	Answer
@microsoft/api-documenter version?	7.47.9
Operating system?	Windows
Documentation target?	Markdown
Would you consider contributing a PR?	No
TypeScript compiler version?	5.6.2
Node.js version (node -v)?	22.7.0