feat: Integrate WireCells previews view into legacy code - WPB-16311

[jullianm]

WPB-16311 [iOS] Integrate WireCells previews in conversation

Issue

This PR integrates WireCellsAttachmentsPreviewView component from WireMessaging into legacy code:

• check whether the message is a multipart message and adjust conditional checking logic
• create the multipart message cell that wraps the SwiftUI previews standalone component
• remove TODOs and clean up code

The previews for chat bubbles simple solution will come later in another PR.

Testing

N/A

Checklist

• Title contains a reference JIRA issue number like [WPB-XXX].
• Description is filled and free of optional paragraphs.
• Adds/updates automated tests.

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UI accessibility checklist

If your PR includes UI changes, please utilize this checklist:

• Make sure you use the API for UI elements that support large fonts.
• All colors are taken from WireDesign.ColorTheme or constructed using WireDesign.BaseColorPalette.
• New UI elements have Accessibility strings for VoiceOver.

[github-actions]

Test Results

2 052 tests   2 025 ✅  2m 19s ⏱️
  336 suites     27 💤
    2 files        0 ❌

Results for commit a91fed1.

♻️ This comment has been updated with latest results.

[samwyndham]

LGTM