SS-40 - MMS Notification Strings

[AL-Session]

Contributor checklist

• I have tested my contribution on these devices:

• Virtual Pixel 3a, Android 9 API 28
• Virtual Pixel 3a, Android 14 API 34

• My contribution is fully baked and ready to be merged as is
  - [X] I ensure that all the open issues my contribution fixes are mentioned in the commit message of my first commit using the Fixes #1234 syntax

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Description

This PR performs the following work:

• Removes three strings (which were never shown to the user in the first place),
• Introduces the Phrase library, and
• Uses the phrase library for substitution of emojis into the attachmentsNotification string ("{emoji} Attachment").

To test this code just send some messages with various file types (images, GIFs, audio, voice messages, etc.) between devices. If the receiving device does not have Session currently active the notification will be displayed containing a relevant emoji, (e.g., "📷 Attachment", etc.).

Additionally, if the receiving device has the Session open but at the home screen then the snippet for that conversation will be updated to use the "📷 Attachment" text (as appropriate for the attachment type).

While this ticket is really part of the Strings chunk of work, I've based this PR on dev because Strings will be worked on for a while longer and needs to have both the Groups and Onboarding chunks merged before it can be finalised (with new strings hooked into the new functionality) before Strings itself can be merged into dev. As such, if I'd based this on Strings it would have grown stale waiting for that to happen as we can't PR this code back into the non-PR'd Strings code!