Preserve array-based StringBuilder.AppendJoin bindings

Group originally expanded StringBuilder.AppendJoin string/object values into an explicit array inside a proven expression-tree lambda before retargeting; also repair zero-value calls whose new span overloads are ambiguous in any context. Preserve the original params-array overload when .NET 9 span params would prevent compilation. Retain ordinary nonempty delegates, normal-array calls, named/generic arguments, comments and conditional snapshots.