Build DCMTK with optional dependencies enabled

The current port of DCMTK does not enable its many optional dependencies. Given many (all?) of these optional dependencies are available in vcpkg, it would be nice to enable them. The main dependencies are:

- libiconv or icu
- libjpeg-turbo
- openjpeg
- libpng
- libxml2
- openssl
- tiff
- zlib

When you install the official DCMTK sources, they provide these dependencies as pre-built binaries + headers, and their CMake scripts can find them. Unfortunately the naming scheme for these pre-built dependencies differs from the standard names, so some CMake patches will be required.