[NT-1754] Surface merge tag functionality in RN implementation

[Alex Freas (akfreas)]

NT-1754 Surface merge tag functionality in RN implementation

• Use merge tag functionality in MergeTagScreen.tsx
• Make available on main App screen
• Update App.tsx, breaking into components

This provides a basic reference implementation for the merge tags in the main React Native implementation app. I have moved the "dev dashboard" functionality out of this PR, it will be reintroduced later on with another ticket.

Here's how the current implementation app looks now:

[David Nalchevanidze (nalchevanidze)]

looks like a huge file. we could also break it down. in utils and rendered components i guess. maybe we can also give bit description what its trying to achieve as its not that clear from first look.

[Charles Hudson (phobetron)]

While I like the extensive documentation, the app may not be the best place to keep it. It's difficult for me to see how a customer would actually implement Rich Text with Merge Tags, due to the focus on having everything partitioned out and documented/tracked separately. It would be nice if we simply rendered the Rich Text with Merge Tags as it would be in a real-life implementation technically, not with real-life content, just bare-bones integration and rendering code.

[Charles Hudson (phobetron)]

👷🏻 🏗️