This decreases our APK size by a few megabytes. Most of the reduction
is from Java libraries that we only use small parts of. Code shrinking
gets rid of all the unused code from these libraries from the APK.

Because I highly value the ability to get stack traces that make
sense, I have specifically disabled obfuscation (automatic renaming
of symbols to short incomprehensible names).

I've only enabled code shrinking for release builds, purely because
I feel like the extra build time (30 seconds on my machine)
would be annoying when you want to make debug builds rapidly.