Add vcpkg package.

[Arthur Sonzogni]

There are several people asking for it:

• microsoft/vcpkg#16327
• https://www.reddit.com/r/cpp/comments/nsu62k/ftxui_c_functional_terminal_user_interface/h0u8lab?utm_source=share&utm_medium=web2x&context=3

[Henrik Gaßmann]

I think this can be closed as microsoft/vcpkg#18360 has been merged.