Context + Feature Description

Currently, python setup.py install --fx-only does not apply for Dynamo due to the presence of certain operators such as torch_tensorrt._Input. Input, device, and other data structures which depend on the C++ portion of the API can be eliminated by making Python-only versions of these data structures in the torch_tensorrt.dynamo module directory. Then, Dynamo can be imported directly using only Python installs, which are much faster and easier than the C++ install.