[android] Convert .png assets to .webp assets

Summary:
This conversion happens during the bundleRelease process and takes a bit of time. Might as well do it once and avoid whatever cost during buildtime.

(This was a "lossless" conversion)

Context: https://developer.android.com/studio/build/optimize-your-build#use_webp

Test Plan: Things continue to look as expected when launching app on Android emulator.

Reviewers: def-au1t, palys-swm, yayabosh

Reviewed By: palys-swm, yayabosh

Subscribers: ashoat, Adrian

Differential Revision: https://phab.comm.dev/D4369