[android] Investigate FABs

[hawkrives]

inspired by discussion in #3182

Android uses FABs (floating action buttons) to draw the eye / finger to certain "primary actions" on a screen.

I'd like to use this issue to discuss what views should use FABs, and which actions should be promoted to FABiness.

We should maintain a checklist in this OP with the current decisions.

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• Student Work: "Open Posting", as a centered, full-width FAB
• Directory detail view: "Call" and "Email" via 📇 Native Directory view #3558

[rye]

react-native-paper was one thing that has FABs nicely-implemented.

[drewvolz]

We've implemented a FAB in the android app but we could still track where we're using it and more use cases for it.