Simplify shading of conscrypt

Currently users who would like to shade conscrypt are required to build the package with the JNI_JARJAR_PREFIX defined which requires all shading of conscrypt to know how to build conscrypt in the first place.

This could be simplified by adopting the pattern done by tcnative where the package prefix path for JNI is [parsed from the library name](https://github.com/netty/netty-tcnative/blob/9fd38de8a07cc413b83cacf39470f2845a68e26c/openssl-dynamic/src/main/c/jnilib.c#L233) allowing for shading of conscrypt without needing to rebuild a custom version.