Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything or linked relevant results below
• I made sure the docs are up to date
• I included tests (or that’s not needed)

Description of changes

This PR tries to map MDX Markdown node to correct JSX node. The feature request is at https://github.com/orgs/mdx-js/discussions/2639 . Before, the MDX node are translated to <></> fragment in language service, which is not typed well (see microsoft/TypeScript#62358) and this PR changes them to a slightly corrected translation, such as <p></p>.

Benefit on this, we can do type-checking on JSX expression 'hole' inside Markdown contents, such as (e.g. translate to React JSX):

Also some open questions:

• The parser returns something like listItem { paragraph { innerContent } } for a compact list item, which is not the correct behavior according to CommonMark spec (says no <p> inside a
• if compact), so the original idea of typing <li> may not work;
• There are no source mappings of plain texts and tag names, so errors from those content's typing will be silenced;
• Documentation updates.