Add vcpkg.json manifest for project dependencies

[damster101]

my vcpkg wouldn't install the dependencies otherwise

[djowel]

There's active development in the artist develop branch, which will be merged to element's develop branch. Can you try that?

It's a major rewrite following the announcement at Discord:

Check out the Artist develop branch. It's a ground up rewrite of artist with various improvements and new features:

vcpkg-based build system — replaces the old prebuilt binary branch; Skia and all dependencies managed via vcpkg with a shared R2 binary cache for fast restores
Cairo backend — HarfBuzz text shaping, software shadow blur, macOS Quartz surface optimisation
Direct2D backend — native Windows D2D/DirectWrite/WIC, no Skia dependency
Native Linux hosts — GTK3, Wayland, and X11
Rope-backed text layout engine — multi-paragraph, incremental edits, O(log n) insert/erase
Visual regression testing — CIEDE2000 perceptual comparison with complexity-adaptive tiled checks
Comprehensive CI — all platforms and backends covered, including headless smoke tests

Heads up! This will be merged to master in the near future.