In addition to changing the build-type dependent build directories, we
can take this opportunity to move the vcpkg cache directory to the Build
folder itself. This probably isn't 100% needed, but it ensures that no
leftover artifacts are used from non-dynamic vcpkg builds, and it's also
generally nice to have all build artifacts under Build.
Most users will be building with Xcode Clang on macOS anyway, as our
build scripts default to the system compiler if it's new enough. We
already have an upstream Clang-based workflow on Linux, so we won't lose
any compiler coverage by switching to Apple Clang on macOS.
This should help us avoid build breakages like #186.
And hook it into ladybird.sh for convenience. The script will set up
PATH and other environment variables automatically.
On CI, vcpkg is theoretically already installed on Linux machines, but
not with the right environment variables, and not on macOS. So this also
makes CI use this script to bootstrap vcpkg.
