Migration: Migrate sets of projects

[brthor]

• Allow for the first argument to dotnet-migrate to be a path (remove -p) (Add support to migrate a directory. cli#4254)
• If that path has a project, use that and it's P2P dependencies (Migrate P2P references cli#4221)
• Otherwise recursively search for projects and their P2P dependencies (Add support to migrate a directory. cli#4254)
• Allow for --global-json or -g to migrate all projects found under a global.json as an alternative to the above options (Fix P2P migration and migrate folders in global.json cli#4305)
• Add switch to opt out of P2P following (Migrate P2P references cli#4221)