Combined file messages - follow-ups

[Antreesy]

• Ref Multiple files sharing support 🖼️+🖼️ - Overview #11411
• Web PRs:
  • design(chat): rearrange file previews in combined message #19005
  • refactor(MessageBody): extract FilePreview rendering to new component #19020
  • fix(chat): show correct previews in messages sent #19004
  • fix(upload): construct referenceId for grouped uploads #19040
  • feat(chat): combine file shares into a single message in UI #18989

Missing / relevant features:

• Rendering support
  • single file share Show previews of files again if supported #19430
• Threads support
  • every posted file in a batch creates a thread - 2nd+ files should be replies
  • replies are hidden in main context view
  • replies are not combined in thread context view
  • temporary messages missing indication
• Reactions support
  • on non-last files ignored, only last message reactions are shown
  • individual reactions can no longer be set on non-last files
• Deletion support
  • only last file message can be removed
  • should be deleted one by one
  • single file deleted/unshared on Files side
• Edit support
  • edit caption only works on the last file
  • adding caption on non-last file will break the grouping
  • edit file itself?
• File actions support
  • 'Go to file/folder', 'Download' always target the first file
  • Individual files can be targeted from Viewer only
• Read receipts support
  • only last file read receipts are visible
• Better upload support
  • retry failed uploads - might no longer be combined
  • race condition between userA sharing and userB posting
• Voice messages support
  • VM excluded from combining entirely
  • VM should not have a caption?
• Reply/Reply privately/Forward support
  • last file is targeted for replying/forwrding
• Navigation support
  • focusMessage feature needs workarounds
• Backward compatibility:
  • An old client without the combining logic will see each message as a separate normal message, with full per-file actions available.