replace `jarsigner` with build tools' `apksigner` which is capable of using newer signature schemes
remove the `android-manifest` flag and assume the file exists in the directory we're bundling
make `android-keystore-alias` and `android-keystore-password` optional.
The former is not needed if there's only one key in the keystore, and the latter will be prompted by `apksigner` if missing
don't change the working directory to the bundled directory to prevent confusion when passing a relative path to
`android-keystore`
add the `res`, `assets`, and `lib` directories to the bundle if they exist in the bundled directory