[FIX] Preview rendering for threaded messages

[gerzonc]

Proposed changes

Fixes how to render preview messages for threaded messages with the new message parser.

Issue(s)

How to test or reproduce

1. Create a thread
2. Send different kind of messages (links, mention someone else, mention yourself, etc.) to the thread with the setting Also send to channel enabled.

No message should render with markdown styling

Screenshots

Before	After

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves a current function)
• New feature (non-breaking change which adds functionality)
• Documentation update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• I have added necessary documentation (if applicable)
• Any dependent changes have been merged and published in downstream modules

Further comments

[diegolmello]

Closed in favor of #3465