Add a rule for finding dedented paragraph lines

[SpecLad]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Problem

I frequently see list items like this:

- Foo
Bar

This is a single item, but it's visually ambiguous (seems like "Bar" could be a separate paragraph). I'd like to have a way to find these and replace them with:

- Foo
  Bar

Current solutions

None that I could find. remark-lint-list-item-content-indent and remark-lint-no-paragraph-content-indent both seem like they could be relevant, but neither of them emits a warning in this case.

Proposed solutions

Add a new plugin, say remark-lint-no-paragraph-content-dedent, that flags situations like this.