[rmw_fastrtps_dynamic_cpp] Typesupport implementation leaks and it relies in conceptually broken cpp

[ivanpauno]

See discussion in:

• Memory leak about not to call placement delete after calling placement new rmw_cyclonedds#219
• Use correct functions to resize and get an item, avoiding memory leaks in typesupport code rmw_cyclonedds#228

#228 can directly be applied here.

[ivanpauno]

@iuhilnehc-ynos @richiprosima FYI

[MiguelCompany]

@ivanpauno @iuhilnehc-ynos I am currently addressing this on this branch

I still want to do more testing before opening a PR for it. Will do that on Monday

[MiguelCompany]

@ivanpauno PR #429 is ready for review. All reinterpret_cast<std::vector<unsigned char> *> have been removed, so I think it also fixes #219