copy complex numbers/vectors/matrices from R to C++ and viceversa

[pachadotdev]

Hi @DavisVaughan

I hope you are doing well.

Happy holidays !

Here is a PR to copy complex numbers from R to C++ and viceversa.

I added multiple tests for complex numbers that pass.

> test()
ℹ Testing cpp11test
✔ | F W  S  OK | Context
✔ |         16 | formatted_errors                                                                                                                                           
✔ |         14 | complex                                                                                                                                                    
⠏ |          0 | cpp                                                                                                                                                        Warning: stack imbalance in 'withVisible', 68 then 64
✔ |        142 | as_cpp-C++                                                                                                                                                 
✔ |        123 | complexes-C++                                                                                                                                              
✔ |         28 | data_frame-C++                                                                                                                                             
✔ |        145 | doubles-C++                                                                                                                                                
✔ |         12 | environment-C++                                                                                                                                            
✔ |          5 | external_pointer-C++                                                                                                                                       
✔ |          6 | function-C++                                                                                                                                               
✔ |         77 | integers-C++                                                                                                                                               
✔ |         52 | list-C++                                                                                                                                                   
✔ |         12 | list_of-C++                                                                                                                                                
✔ |         64 | logicals-C++                                                                                                                                               
✔ |         72 | matrix-C++                                                                                                                                                 
✔ |          4 | nas-C++                                                                                                                                                    
✔ |          2 | unwind_protect-nested-C++                                                                                                                                  
✔ |          9 | unwind_protect-C++                                                                                                                                         
✔ |         25 | r_complex-C++                                                                                                                                              
✔ |         36 | r_vector-capabilities-C++                                                                                                                                  
✔ |         90 | r_vector-C++                                                                                                                                               
✔ |         49 | raws-C++                                                                                                                                                   
✔ |          4 | sexp-C++                                                                                                                                                   
✔ |          2 | string-C++                                                                                                                                                 
✔ |         78 | strings-C++                                                                                                                                                
✔ |          9 | doubles                                                                                                                                                    
✔ |          6 | matrix                                                                                                                                                     

══ Results ═════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════
[ FAIL 0 | WARN 0 | SKIP 0 | PASS 1082 ]

Perhaps @krlmlr and @Antonov548 find this interesting :)

[pachadotdev]

it would be good to merge this PR and then adapt the tests here