[RFC] Add WIC image loader and WinHTTP-based network backend

[saitoha]

This patch adds a WIC (Windows Imaging Component) based image loader and a WinHTTP-based network backend (as an alternative to libcurl) for Windows builds.

The WIC-based loader can be helpful when dealing with image formats not otherwise supported, particularly .ico and .webp.

Unlike curl, WinHTTP supports only two protocols - HTTP and HTTPS - but its lack of external dependencies makes it a good fit from a portability standpoint.