Good end-to-end Windows support

[cgravill]

We want to have good end-to-end support for Windows from PyTorch through Knossos, and returned optimised functionality.

We're starting from a decent position as we've had builds including Windows for parts of the project.

• build PyTorch extension with KSC generated code with MSVC MSVC compatibility adjustments #652
  • allow ksc to directly build with MSVC as well
• enable running or skip Python tests on Windows Most python tests windows #662
• run current TS2K automated test on Windows TorchScript to Knossos test with preview PyTorch on GitHub Actions #669 Jax on Windows comparison #665
  • out of memory issues on multiple tests - likely to apply to Linux as well but not triggered Out of heap space on multiple PyTorch tests #679 mitigated with Separate process per test for TS2K Windows tests #706
• run on a current version of PyTorch - 1.8 failures PyTorch 1.8.0 MSVC #659 PyTorch 1.8.1 #683
• nightly preview builds of TS2K to ensure the PyTorch C++ keeps working for our usage TorchScript to Knossos test with preview PyTorch on GitHub Actions #669
• contribute documentation fixes back to PyTorch to improve overall C++ PyTorch on Windows

[cgravill]

@awf any Windows tasks to add?