Start DM on first message

[weeman1337]

ToDo

• implement error handling
• all tasks from the comments
• test
  • verification from room member list
  • click message in room member list

After merge:

• Display something meaningful if opening a local room URL for an unknown room → create new issue

Test checklist

• Start DM from new spotlight search
• DM with single MXID
• DM with multiple MXID
• DM with single 3PID (e-email)
• DM with mixed IDs
• Start DM with
  • Text message
  • Sticker
  • Location
  • Live location
  • Poll
  • Voice message
  • Attachment
    • Upload via composer button
      • Single file
      • Multiple files
    • Drag & drop
      • Single file
      • Multiple files
    • Paste from clipboard
      • Single file

Closes element-hq/element-web#14736

PSD-249

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Here's what your changelog entry will look like:

✨ Features

• Start DM on first message (#8612). Fixes Only create DM room when first message is sent element-hq/element-web#14736.

[giomfo]

@weeman1337 FYI I tried it in the Netlify deployment. This is a very good start
I observed one point that we can fix easily, the local room should not be displayed if an actual DM is already existing for the selected contact. In your current implementation, I switch on the actual DM after I fill my message in the local/fake room

[SimonBrandner]

(wrong PR - sorry!)

[weeman1337]

For the reviewers: This PR is now ready for review.