A preview tab for markdown fields

### Describe the problem

I am not sure if the comment would be presented as what I expected since I am not quite familiar with the Markdown syntax used by Weblate.
Sometimes I would forget to add some formatting symbols.

### Describe the solution you'd like

Adding a preview tab for the comment field.

The comment field of Greasy Fork is a good example: https://greasyfork.org/scripts/4255/feedback#post-discussion

### Describe alternatives you've considered

An additional text formatting toolbar (that is GitHub-like) would be appreciated.

### Screenshots


### Additional context

_No response_