Depend on tiny_obj_loader 2.0 via conan

Currently tiny_obj_loaded is included as a simple header file. Conan doesn't support prerelease versions, so until 2.0 is done we need to depend on the header file.

Start by inspecting how the bundled tiny_obj_loader header is included and where Conan dependencies are configured. Check whether Conan can resolve tiny_obj_loader 2.0, then verify that the project still builds using the Conan dependency instead of the header file.

Written by the indexing model from the issue text.