[native] Prevent CoolOrNerdModeSelection emojis from rendering with opacity on Android

Summary:
I noticed that the emojis in the CoolOrNerdModeSelection screen were kind of blurry. I did some Googling and found this solution.

On iOS, setting the text color of emojis has no effect. On Android, setting the text color of emojis to black seems to make them render with full opacity.

Depends on D8002

Test Plan:

before	after

Also tested on iOS to confirm no changes. Note that the registration flow only supports dark mode, but it appears that color: 'black' has the same impact on Android in either mode.

Reviewers: atul, ginsu

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8003