Improve migration of intersection types

[SupunS]

Update the static type migration to convert owned intersection types

• T{} / Any*{} to T/Any*

  If the intersection type has no interface types, then return the legacy type as-is.

  This prevents the migration from creating an intersection type with no interface types, as static to sema type conversion ignores the legacy type.

• Any*{A,...} -> {A,...}

  If the intersection type has no or an AnyStruct/AnyResource legacy type, and has at least one interface type, then return the intersection type without the legacy type.

• T{A,...} -> T

  If the intersection type has a legacy type, and has at least one interface type, then return the legacy type as-is.