…brary.

Extract a `runTool` function that captures the stdout and returns it.
A small refactoring that reduces copied code.

Uses two pre-existing packages to run some simple queries on a javascript
database.

1. Better malformed data guard for PackDownloadOutput
2. Fix Packs type
3. Remove TODO in init-action

This commit adds a `packs` option to the codeql-config.yml file. Users
can specify a list of ql packs to include in the analysis.

For a single language analysis, the packs property looks like this:

```yaml
packs:
  - pack-scope/pack-name1@1.2.3
  - pack-scope/pack-name2   # no explicit version means download the latest
```

For multi-language analysis, you must key the packs block by lanaguage:

```yaml
packs:
  cpp:
    - pack-scope/pack-name1@1.2.3
    - pack-scope/pack-name2
  java:
    - pack-scope/pack-name3@1.2.3
    - pack-scope/pack-name4
```

This implementation adds a new analysis run (alongside custom and 
builtin runs). The unit tests indicate that the correct commands are
being run, but I have not actually tried this with a real CLI.

Also, convert `instanceof Array` to `Array.isArray` since that is
sightly better in some situations. See:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray#instanceof_vs_isarray

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.

Fix grouping of the analysis logs, so that custom query logs also get grouped.
Capture the stdout of codeql database analyze, which contains the analysis summary
from summary and diagnostic queries.
Log this output in its own group, along with the baseline computed in the Action.