fix(mdxish): stop lone leading dash from becoming list in magic block cells

[maximilianfalco]

🎫 Resolve RM-16239

🎯 What does this PR do?

Magic block table cells (e.g. [block:parameters]) that contained a lone leading -, *, or + followed by a space were being parsed by the cell content parser as a bullet list, producing an empty <ul><li> instead of the literal text the author wrote.

The fix escapes leading list markers in parseTableCell before handing the cell text to the content parser, so the markers render as plain text while emphasis (*foo*, where the marker hugs the text with no trailing space) still parses correctly.

🧪 QA tips

[block:parameters]
{
  "data": {
    "h-0": "-",
    "h-1": "-",
    "0-0": "- fqefeq",
    "0-1": "- hello"
  },
  "cols": 2,
  "rows": 1
}
[/block]

the cells containing - only should be rendered as plain text instead of an empty list node

📸 Screenshot or Loom