launchSettings.json should be shareable and configuration dependent

Currently there is no easy way to share launchSettings.json file. You need to create your own target and copy it into the project directory, which is far from ideal. Right now in corefx we live build the launchSettings.json file when building the test assembly with input and outputs (to not overwrite user inputs after a sequential build): https://github.com/dotnet/buildtools/blob/0c10cac8b187e43fc8782975465a0474fcb0d3c3/src/Microsoft.DotNet.Build.Tasks/PackageFiles/tests.targets#L613

Also it would be great if we could have profiles based on selected configurations. Ie I want to see profile A and C when the netcoreapp configuration is selected and B and D when netfx is selected. Either via a property inside the launchSettings.json file or by having different files depending on the configuration.

cc @weshaggard @eerhardt @BillHiebert @davkean