According to prebuilts/android-emulator/README:
This directory contains prebuilt emulator binaries that were generated by running the following command on a 64-bit Linux machine:
external/qemu/android/scripts/package-release.sh
--darwin-ssh=
--copy-prebuilts=
Which is also what I found in Where is the Android emulator source code but this repo is not updated since 2015
So, where is the android emulator code hosted right now?