Make ReservedPortNames a static array, so accessing it from a static BTFactory doesn't crash

[corot]

I'm remaking our codebase so BT nodes can self-register with static initialization.
But I get this rather cryptic error:

(gdb) bt
#0  0x00005555556290a1 in std::__detail::_Mod_range_hashing::operator() (this=0x5555556c1f40 <BT::ReservedPortNames>, __num=2133999577744268061, __den=0) at /usr/include/c++/9/bits/hashtable_policy.h:433
#1  0x0000555555639b68 in std::__detail::_Hash_code_base<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__detail::_Identity, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, true>::_M_bucket_index (this=0x5555556c1f40 <BT::ReservedPortNames>, __c=2133999577744268061, __n=0) at /usr/include/c++/9/bits/hashtable_policy.h:1390
#2  0x0000555555637240 in std::_Hashtable<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Identity, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, true, true> >::_M_bucket_index (this=0x5555556c1f40 <BT::ReservedPortNames>, __k="msec", __c=2133999577744268061) at /usr/include/c++/9/bits/hashtable.h:676
#3  0x0000555555634b48 in std::_Hashtable<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Identity, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, true, true> >::count (this=0x5555556c1f40 <BT::ReservedPortNames>, __k="msec") at /usr/include/c++/9/bits/hashtable.h:1485
#4  0x0000555555630df3 in std::unordered_set<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::count
    (this=0x5555556c1f40 <BT::ReservedPortNames>, __x="msec") at /usr/include/c++/9/bits/unordered_set.h:669
#5  0x000055555562e77e in BT::CreatePort<unsigned int> (direction=BT::PortDirection::INPUT, name=..., description=...) at /home/jorge/catkin_ws/executive/src/btcpp/include/behaviortree_cpp_v3/basic_types.h:274
#6  0x00007ffff796e65a in BT::BehaviorTreeFactory::BehaviorTreeFactory() () from /home/jorge/rapyuta_ws/io_amr/devel/lib/libbehaviortree_cpp_v3.so
#7  0x00007ffff72c6838 in __static_initialization_and_destruction_0 (__initialize_p=1, __priority=65535) at /home/jorge/rapyuta_ws/io_amr/src/rr_navigation/rr_nav_servers/src/nas_strategy.cpp:68
#8  0x00007ffff72c6a9f in _GLOBAL__sub_I_nas_strategy.cpp(void) () at /home/jorge/rapyuta_ws/io_amr/src/rr_navigation/rr_nav_servers/src/nas_strategy.cpp:312
#9  0x00007ffff7fe0b9a in call_init (l=<optimized out>, argc=argc@entry=5, argv=argv@entry=0x7fffffff9c98, env=env@entry=0x7fffffff9cc8) at dl-init.c:72
#10 0x00007ffff7fe0ca1 in call_init (env=0x7fffffff9cc8, argv=0x7fffffff9c98, argc=5, l=<optimized out>) at dl-init.c:30
#11 _dl_init (main_map=0x7ffff7ffe190, argc=5, argv=0x7fffffff9c98, env=0x7fffffff9cc8) at dl-init.c:119
#12 0x00007ffff7fd013a in _dl_start_user () from /lib64/ld-linux-x86-64.so.2

tbh, I have no clue why the current code doesn't work, being ReservedPortNames a global variable.
Looking at the error, must be something about hashing the strings.
This PR avoids the problem entirely by using an array instead of a unordered_set

[facontidavide]

implemented differently