Add logging throughout the extension

[brettcannon]

And VS Code should have something for this in their March release.

• Ensure errors logged in extension are not (via some config or ability to mock) logged during unit tests
  (else this pollutes the test output and could be confusing).
  Note: Errors are forcibly raised in unit tests.

[brettcannon]

Any place we execute something behind the scenes through a system call we should document, e.g. the command we use to discover tests, to run them, etc.

[brettcannon]

Duplicate of #2156

[kimadeline]

Todo

• log all extension commands being run behind the scenes in the Python output panel, except for testing (stays in its own testing window)
• for every command being run, display

> path/to/command -args -args2
cwd: current/working/directory // optional line if there is no directory parameter passed to the logging function

• make sure that the commands and their output are being logged in VSCode's devtools
• Ensure errors logged in extension are not (via some config or ability to mock) logged during unit tests
• check that it works for:
  • vcode single workspaces
  • vscode multi-folder workspaces
  • folders
  • single files

Later/separate PR:

• move language server logs to a separate LS channel (might be related to Add command to display the language server output panel #7459)
• display a truncated output in the Python channel (to revisit)

[ericsnowcurrently]

I've verified that, using master, I now see commands logged in the "Python" output panel.