We previously included this option conditionally when users were replying
or creating a new topic while they had content already in the composer.
This makes the dialog always include three buttons:
- Close and discard
- Close and save draft for later
- Keed editing
This also changes how the backend notifies the frontend when there is
a current draft topic. This is now sent via the `has_topic_draft`
property in the current user serializer.
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