Honor the `white-space: pre` comment hint for plain text nodes

`printTextNode` always reflowed text as an HTML paragraph, collapsing
single newlines into spaces. That's correct for real HTML text, but it
silently ignored the documented `{% # white-space: pre %}` comment
hint, so there was no way to opt a bare text node out of it. This
mangled files with meaningful line breaks but no HTML tags, such as a
templates/robots.txt.liquid override.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01F9pHQHyQvE1bP26XUkfmSj