Also, move `getTemporaryDirectory` back to `actions-util`.

Must access the env var directly in order to avoid recursive calls to 
`getRequiredEnvParam`.

This is a functionality that never worked perfectly and hasn't been
used for a while.

This allows developers to run the action on their local machine, but
the run was always flaky and never 100% mirrored what was happening on
the actions runner.

This PR ensures environment variables are set before any invocation of
the CLI.  Here is a list of vars that are set:

https://github.com/github/codeql-coreql-team/issues/1124#issuecomment-852463521

This ensures the CLI knows the features and versions of the containing
actions/runner.

Additionally:

- Fix the user agent so that it more closely aligns with user agent
  spec
- Refactor environment variable initialization so that it all happens in
  one place and call.
- Move Mode, getRequiredEnvParam, setMode, getMode out of actions-util
  and into util. actions-util is meant for utils only called by the
  action, not the runner.

The `prepareLocalRunEnvironment()` method is most likely deprecated and
should be removed. I originally added it because I had a way of working
where I would run the action from my local machine to test out changes,
but this was always a little flaky. So, I no longer use this way of
working. I will probably remove it soon.

This commit changes the way the action determines if running in action
or runner mode. There is now an environment variable that is set at the
beginning of the process and elsewhere in the process, we can check to
see if the variable is set.

Fixes a bug where we were looking for incorrect keys for metrics rules.
Previously, we were using full language names in the keys. Now, we use
the short language names in the metric ids. This is done through a
simplification of the code.

Also, this change does two smaller things:

1. Prints out the baseline count to the logs
2. Adds the `assertNever` function to ensure we never miss a case in
   a switch statement. This function is borrowed from vscode-codeql.

spelling: executable
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Signed-off-by: Josh Soref <jsoref@users.noreply.github.com>

Mitigation for OOM errors (137/SIGKILL) seen by users when we overcommit the available memory.
For Unix, reserve 1GB.
For Windows, reserve 1.5GB, as the OS needs more memory and estimates inaccurately.

This commit adds two new ways of specifying GitHub auth:

1. from the GITHUB_TOKEN environment variable
2. from standard input

This commit does not include any documentation changes and the
descriptions of new command line options will need to be tweaked.

…sarif output