Add etwtrace as a build dependency and bundle it

[AdamYoblick]

The etwtrace package lives at https://pypi.org/project/etwtrace/

• Download the package inside of PreBuild.ps1 and use install_wheels.py to install and merge the wheels into the packages folder, into a non-versioned folder called etwtrace
  • This needs to be a "fat" install, taking in files from all the wheels, since we don't know what platform/python version the user will have, so we package all of them, just like debugpy.
• Modify the build scripts to grab this new folder and include the files in one of the vsix files.