Finish up UI improvements for reply previews

[kevinaboos]

• [x] fix reply button styling and direction
• [x] fix the issues with usernames and message content not displaying, which is related to how Robrix carefully caches already-drawn timeline events. I'll tackle this shortly.
• [ ] fix various "TODO"s listed in the code that are related to styling buttons/other UI items.
• [x] fix horizontal alignment of Condensed* messages -- they're no longer left-aligned with regular messages
• [x] set cursor: Hand for the ReplyingPreview widget to make it more obvious that they're clickable w/ actions.
  • Huh, this was actually already set, but it's not displaying the cursor as intended. Probably an issue with PortalList or Makepad's hover actions, which have been fixed in a recent version that Robrix hasn't yet upgraded to.
• [ ] for the action ReplyPreviewClicked, we need a few things:
  • [ ] include the unique event ID to handle the case where the replied-to message hasn't been retrieved from the server (via pagination) and isn't yet locally available.
    • This is actually quite complex to deal with, so maybe we can save it for a future issue, and for now we can simply log a warning that says something like "TODO: jumping back to a replied-to message that isn't yet locally retrieved is currently unsupported"
  • [ ] a smooth scrolling action that scrolls upwards to that message rather than an abrupt jump (Makepad's PortalList may not yet support this?)
  • [ ] highlighting or temporarily flashing the background (maybe light blue or green) to indicate which specific message was the one being shown in the just-clicked ReplyingPreview
• [x] fix avatar font sizing in ReplyingPreview to be properly scaled down.
• [x] shift the inline reply preview (the one above the message) to the right a bit such that the vertical bar is aligned with the middle of the avatar picture.
• [x] Refactor the populate_message* logic such that it can be easily re-used for populating the content of a ReplyingPreview. I will also tackle this.

[kevinaboos]

PR #138 addressed these two:

shift the inline reply preview (the one above the message) to the right a bit such that the vertical bar is aligned with the middle of the avatar picture.

fix horizontal alignment of Condensed* messages -- they're no longer left-aligned with regular messages