* ci: Add vcpkg submodule
* cmake: Fix NSIS not detecting platform arch
* cmake: Add QTDIR(64|32)
This change adds a new var for QTDIR(32|64) which makes it easier
to specify a specific directory for Qt, rather than having to edit
the prefix path directly, which can get pretty messy. Functionally,
this shouldn't affect any builds that are already finding Qt as
part of path, and should not affect Linux/macOS.
* cmake: Bump min cmake version
* ci: Add GitHub Actions for Windows
