Add inspect-library helper

This is the WIP for the "Executable to dlopen and inspect a library" of T15426.

This is an output example of the current version:

$ ./x86_64-linux-gnu-inspect-library libzvbi.so
{
  "libzvbi.so": {
    "path": "/usr/lib",
    "dependencies": [
      "/usr/lib/libzvbi.so",
      "/usr/lib/libm.so.6",
      "/usr/lib/libpng16.so.16",
      "/usr/lib/libz.so.1"
    ]
  }
}

The next thing to do that is still missing is to take a list of (version, symbol) pairs as input.