fix(stripComments): not escape checkbox

[eaglethrost]

	Fix CX-2979

🧰 Changes

Checkboxes are currently not being rendered in non-admin view when sanitise comment is on (in all legacy, mdx, mdxish projects). The root cause of this is because of the remarkParse and remarkStringify plugins in the stripComments pipeline which escapes [ ].

The fix is to utilise the micromark plugin mdast-util-gfm-task-list-item that specifically parses checkboxes correctly in the pipeline. This should be safe to do as it's just an extension of the pipeline. The reasons of why this is not an issue in mdx or mdxish is because it uses remark-gfm which already included that plugin.

Before	After

🧬 QA & Testing

1. Create a document with some checkboxes, such as:

- [ ] empty checkbox
- [x] ticked checkbox
- \[ ] escaped bracket should still not be converted to checkbox
- [ afa ] should not be converted to checkbox

2. In the markdown playground, test the input with strip comments option on, and test with legacy, mdx, and mdxish rendering engine.
3. The checkboxes should get rendered and not just be plain [ ]. There should also be no rendering difference in the 3 engines with strip comments on