Structs with variable length inline arrays MUST be blittable

[AArnott]

An array that contains a variable length inline array (e.g. RTM_ENTITY_EXPORT_METHODS) must be blittable because custom memory management is the only way to handle it.
We should recognize this and emit a blittable (non-marshaled) version even when AllowMarshaling is set to true.

If that same struct contains other fields that require marshaling, perhaps we just error out when emitting because it's an impossible thing to properly support.

[AArnott]

With #292 fixed, we have the tools necessary to recognize and require that a struct be unmanaged (i.e. blittable). For this issue then, we should recognize that the structs identified in this issue are among those that trigger the blittable requirement.
We could change our IsManaged test to return false for these structs since a managed version will never be emitted, thereby avoiding the suffix that would otherwise be appended to it.