Part of [[ https://linear.app/comm/issue/ENG-3966/rename-the-holder-message-field-to-bloburi | ENG-3966 ]]
This is a controversial diff, the approach is [[ https://linear.app/comm/issue/ENG-3966#comment-42fd695b | discussed in comments ]].
Detailed description and all TODO follow-ups are tracked in [[ https://linear.app/comm/issue/ENG-4285/revert-the-any-casts-in-message-reducer | ENG-4285 ]]. As soon as RN / Flow is upgraded, these should be reverted.
Depends on D8370