migrate-xunit-to-xunit-v3

Migrates .NET test projects from xUnit.net v2 to xUnit.net v3. USE FOR: upgrading xunit to xunit.v3. DO NOT USE FOR: migrating between test frameworks (MSTest/NUnit to xUnit.net), migrating from VSTest to Microsoft.Testing.Platform (use migrate-vstest-to-mtp). For xUnit v3 MTP filter syntax (--filter-class, --filter-trait, --filter-query), also load migrate-vstest-to-mtp.