IVGCVSW-4487 Remove boost::filesystem

IVGCVSW-4487 Remove boost::filesystem

 * Replace filesystem::path
 * Replace filesystem::exists
 * Replace filesystem::is_directory
 * Replace filesystem::directory_iterator
 * Replace filesystem::filesystem_error exception
 * Replace filesystem::temp_directory_path
 * Replace filesystem::unique path
 * Replace filesystem::ofstream with std::ofstream
 * Replace filesystem::remove
 * Replace filesystem::is_regular_file
 * Replace boost::optional with armnn::Optional in touched files
 * Remove some superfluous includes
 * Update build guides, GlobalConfig.cmake and CMakeLists.txt
 * Remove redundant armnnUtils::Filesystem::Remove function.
 * Remove redundant armnnUtils::Filesystem::GetFileSize function.

Temporarily adding back Boost::filesystem to enable Boost::dll.

Signed-off-by: Francis Murtagh <francis.murtagh@arm.com>
Signed-off-by: Colm Donelan <Colm.Donelan@arm.com>
Change-Id: Ifa46d4a0097d2612ddacd8e9736c0b36e365fb11