Try bundling fonts

[gnprice]

Zulip web uses the font Source Sans 3 for most text, and Source Code Pro for code blocks and code spans.

Currently, in zulip-flutter as well as in the zulip-mobile RN app, we use system fonts. This has advantages but also disadvantages:

• Bundle a font in the app and use it consistently zulip-mobile#2447
• Solution found: Newer Unicode emojis don't render on older Android devices zulip-mobile#3885

It would be neat to try using the same fonts as on web. Here's Flutter upstream's cookbook recipe for using a custom font:
https://docs.flutter.dev/cookbook/design/fonts

[chrisbobbe]

Linking/quoting a relevant discussion on CZO: https://chat.zulip.org/#narrow/stream/243-mobile-team/topic/flutter.3A.20.23F64.20bundling.20fonts/near/1570370

Android has a feature called "Downloadable Fonts":

The Downloadable Fonts feature lets APIs request fonts from a provider application instead of bundling files into the app or letting the app download fonts. Downloadable Fonts is available on devices running Android API versions 14 and higher through the AndroidX Core library.

Downloadable Fonts offers the following benefits:

• Reduces the app size, therefore increasing the app installation success rate.
• Improves the overall system health, as multiple apps can share the same font through a provider. This saves users cellular data, phone memory, and disk space. In this model, the font is fetched over the network when needed.

It seems possible in theory to use this feature and get those advantages; see a sketch of how we might try: https://chat.zulip.org/#narrow/stream/243-mobile-team/topic/flutter.3A.20.23F64.20bundling.20fonts/near/1570476

But it doesn't currently seem worth the effort for us: https://chat.zulip.org/#narrow/stream/243-mobile-team/topic/flutter.3A.20.23F64.20bundling.20fonts/near/1570489