Support function pointers as a supported variable type

[mahaloz]

In the fdupes binary in the test cases, one function, 11475, has _func_int_file_t_ptr_file_t_ptr* as a variable type. When using the get_dependencies API in the deci, it is not included.

To support this type, we need to add the following:

• When looking up user-defined types, include all the functions with names as possible types
• The type should be of type FunctionHeader
• Figure out how to abstract it to multiple decompilers later. Maybe make a place holder when lifting in libbs to say something like func_ptr_0xdead, then when it get's lowered convert that into whatever the local name in the decompiler is.