Move class_typet::baset to struct_typet

[tautschnig]

Structs can have base classes/structs. This enables wide use of the bases() API.

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[kroening]

Does it make sense to have a middle layer -- struct_with_base_typet or so?
Most users of stuct_typet do not need protection or inheritance.

[tautschnig]

Does it make sense to have a middle layer -- struct_with_base_typet or so?

Maybe - what is the cost of having this API in there, and thus the added value of struct_with_base_typet?

[smowton]

On the other hand does C++ really distinguish a class from a struct at all? I appreciate there are two keywords, but isn't a struct just a class with default public visibility, and the real distinction is between plain-old-data (C-ish structs) any anything else?

[tautschnig]

On the other hand does C++ really distinguish a class from a struct at all?

I'd say the only difference is, as you said, the default access. Which has been clarified in #3002 (cf07c6c).

[allredj]

Passed Diffblue compatibility checks (cbmc commit: c6a55e7).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/85748394

[peterschrammel]

get_identifier() if possible?

[allredj]

Passed Diffblue compatibility checks (cbmc commit: 1f5e03c).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/85823211