* c++: Add command line option to add extra includes to gen files

Fixes #5351
We have an ability to pass custom types for strings, allocators, etc
but have no way to tell the generator to include the classes in gen code

* c++: remove std::strtok for std::string methods. passes msvc compile

* generate_code.sh: add --cpp-includes to the test gen script

* tests:generate.bat: update code gen scripts w/ --cpp-includes

* cpp: use command line parsing for extra includes

s/--cpp-includes/--cpp-include/g
Simplify command line parsing of includes by using a std::vector.

* cpp: idl.h: move std::vector for cpp_includes as the last member

msvc does not understand initalization list on our CI server

* cpp:msvc: CI fails on for-range loops

* cpp:codegen: fix error reporting on flatcc

* as per code review: remove unwated --cpp-include in the
tests/generate_code.{sh,bat}