Make MsBuild Vcpkg integration automatically bootstrap vcpkg

[MichalPetryka]

When using VCPKG as a submodule with the MsBuild target files for integration, programmers must manually run the bootstrap script before the first build or after every tool update.

Having it automatically detect the need for doing so and performing it in the background would streamline the usage and remove unclear error messages about vcpkg not being bootstrapped.

I'm not really sure what's the reason for not doing this already, perhaps it has something to do with any options needing to be passed to the bootstrap script?