* Treat lists with a single empty item as plain text, not Markdown.
This allows users to send simple messages such as `-`, `+`, `*` and
`2021.` without Element Web mangling them into a nonsensical empty list.
As soon as any non-whitespace content is added to the item, it switches
back to treating it as a list of one item.
Fixesvector-im/element-web#7631.
* Fix type errors.
* Lint.
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Co-authored-by: Michael Weimann <michaelw@matrix.org>
Co-authored-by: Johannes Marbach <johannesm@element.io>
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