Load visualStudioInstallationParameters from exported VS install config

[ryanbrandenburg]

Currently we have a very long list of required VS components in azure-pipelines-integration-dartlab.yml. It's been suggested that we could export our VS install configuration and put it in the /eng folder. This also has the benefit that we might be able to use that in an InstallVisualStudio.ps1 script to make getting started on the repo easier.