Fix blank TensorBoard pane due to existing MIME type misconfiguration on Windows

[joyceerhl]

TensorBoard has received multiple reports of this even in the browser, so this impacts all TensorBoard users, not just VS Code TensorBoard users.

We have documented how to diagnose and fix this problem: https://github.com/microsoft/vscode-python/wiki/Troubleshooting-TensorBoard-integration-in-VS-Code#integrated-tensorboard-sessions

TensorBoard added a workaround for it that ships with the source code. tensorflow/tensorboard#3128

For whatever reason that's not working and is still hitting our customers on Windows. Ideas:

1. Revisit the fix upstream. Maybe more is needed?
2. Check for and overwrite bad Windows registry values ourselves.

[joyceerhl]

Duh, the upstream workaround wasn't applied because we launch TensorBoard using the launch() function (which is their Python API for starting TensorBoard sessions), and that codepath doesn't contain their workaround. We just needed to apply the same workaround in our launcher script.

[DomInvivo]

Hello @joyceerhl , despite having the latest version of the Python extension, Tensorboard stays blank. I'm working on Windows, but I am connected via SSH to a remote machine running Ubuntu.

What are the steps required to make Tensorboard work?