feat(ew): handle read-only users correctly in EW

[usman-khalid]

Must land with adobe/da-nx#616

Handles read-only access in EW correctly.

• Add a lock icon (and update DA to the newer s2 lock icon for consistency) in the EW canvas header.
• Remove undo/redo buttons for read-only users
• Don't render toolbars for read-only users since they can't make any updates
• Prevent read-only users from making edits that silently fail or never persist:
  • Phantom text updates in layout mode that are never persisted
  • Remove image drag & drop for read-only users, which fails silently with a 403, giving the user a false impression they could take that action

Fixes #1107

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Commits

• 4a5ade5 ✅ (latest)
• 8912194 ✅
• fb42f74 ✅
• 646d2f3 ✅

[sharanyavinod]

@usman-khalid Thank you for the contribution! Code looks good, just have a minor comment.
Also, there are a couple e2es failing related to the changes introduced, so could you take a look at those as well please?