When building retdec, no dependencies should be rebuilt

It is extremily inconvenient that the build system fetches the dependencies and builds them. It is very wasteful in the terms of both time and computer resources and it is completely unsuitable for packaging. Instead prebuilt shared libs and headers packages should be used. I don't mean conan or nix or vcpkg, I mean the packages from the distro for the case of a *nix distros and just dirs which paths a user should provide for Windows. No FetchContent, please.

Start by tracing how the build system currently fetches and builds dependencies, with particular attention to FetchContent and the packaging workflow. Determine the supported distro packages and the user-provided dependency directories for Windows; done means dependencies are not rebuilt and the project can be packaged without FetchContent.

Written by the indexing model from the issue text.