Paragraph whitespace

[bachbui]

This PR updates the Commonmark renderer to support documents containing unicode emspaces (\u2003). There are two relevant changes:
When rendering Paragraphs, we were stripping all leading and trailing whitespace characters from their text to prevent the possibility of these characters being interpreted as markdown symbols, as leading spaces might be interpreted as an indented code block and trailing spaces might be interpreted as a line break. We were being overzealous in this stripping, as MD only considers certain whitespace characters as meaningful in this way. We obtained a narrower set of characters to strip by considering the chars which are matched by [\s], [ \f\n\r\t\v\u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff], and checking which of these are meaningful to markdown.
Secondly, we need to encode unicode whitespace characters as html entities in the rendered output, as otherwise many markdown parsers (including Markdown-it) will ignore them. This PR does that for emspace characters only, but other unicode whitespace characters can be added as needed in subsequent PRs.

[bachbui]

@gnorsilva I've made a dev build for you to test out these changes if you'd like. You can bump these to these packages versions:
@atjson/renderer-commonmark@0.21.14-dev.0
@atjson/source-commonmark@0.21.13-dev.0

[gnorsilva]

Looks good, checked in copilot-atjson and this fixes the issue 👍

[tim-evans]

This is lovely! Thanks for handling this so quickly @bachbui

I'm going to create a follow-up issue to track other non-breaking spaces that we should handle :)

[bachbui]

@gnorsilva This has been merged and released
@atjson/renderer-commonmark@0.21.14
@atjson/source-commonmark@0.21.13