/usr/lib/x86_64-linux-gnu/libdouble-conversion.so is in libdouble-conversion-dev 2.0.1-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libdouble-conversion.so.1
/usr/lib/x86_64-linux-gnu/libdouble-conversion.so.1