Add offset checks when checking that 3D type refines a C type

[nikswamy]

Cf. https://project-everest.github.io/everparse/3d-lang.html#checking-3d-types-for-correspondence-with-existing-c-types

We currently only add sizeof checks; we should also add offsetof checks.

[tahina-pro]

Thanks Nik!
Right now #144 is enough for most cases, but does not seem to work with #if . To this end, we should:

• Generate offsetof for nested anonymous structs and casetypes
• Make the generated StaticAssertions.c file include the .h file provided by the user (in the configuration file given as --config) where compilation constants are meant to be defined