Add environment variables to signal feature and version to the CLI

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.

src/codeql.ts

@@ -11,11 +11,7 @@ import { default as queryString } from "query-string";
 import * as semver from "semver";
 import { v4 as uuidV4 } from "uuid";
 
-import {
-  isRunningLocalAction,
-  getRelativeScriptPath,
-  isActions,
-} from "./actions-util";
+import { isRunningLocalAction, getRelativeScriptPath } from "./actions-util";
 import * as api from "./api-client";
 import * as defaults from "./defaults.json"; // Referenced from codeql-action-sync-tool!
 import { errorMatchers } from "./error-matcher";
@@ -149,7 +145,7 @@ function getCodeQLBundleName(): string {
 }
 
 export function getCodeQLActionRepository(logger: Logger): string {
-  if (isActions()) {
+  if (util.isActions()) {
     return CODEQL_DEFAULT_ACTION_REPOSITORY;
   } else {
     return getActionsCodeQLActionRepository(logger);