Consider using vswhere to find Visual Studio installation

[magicalcookie]

Right now the code in MSVSVersion.py uses the registry to find the Visual Studio installation.
I re-installed my windows 10 recently and only installed the latest copy of Visual Studio 2019, as it turns out none of the registry keys being checked exist on my machine.

I suggest checking for the default location of vswhere.exe and downloading it if it's not there, so we use that to find the Visual Studio installation.

Is this something that makes sense here, I would be happy to implement this and submit a PR.

[refack]

Great minds... I already have a patch in the works https://github.com/refack/GYP/blob/c9aad58fb672f5e40847c5740e26f879da8373a0/gyp/common.py#L742-L759