**What happened?**
Previously we just checked the immediate parent
to see if the module was being included from eslint.
Now we recursively check all the parents.

Also moves this eslint check to it's own config/helper

Introduces the ability to enable webpack DLL support by passing
the flag WEBPACK_VENDOR_DLL=true while running webpack or
webpack-dev-server.

This removes the usage of IS_GITLAB_EE
and prefer to use FOSS_ONLY that has
the following states:
1. nil/empty string: use CE or EE depending on sources
1. false: use CE or EE depending on sources
2. true: use CE always

Currently:
1. If `IS_GITLAB_EE=` is used, it fails to generate Webpack
   as it cannot be parsed as JSON,
2. If `IS_GITLAB_EE=1` is used, it fails on GitLab CE,
3. If `IS_GITLAB_EE=0` it does work correctly, and disables EE,
4. If `IS_GITLAB_EE=1` is used on GitLab EE it effectively required
   to run on EE changes.

This changes to:

Make `IS_GITLAB_EE=` to donate the intent to disable or enable EE
sources, instead of requiring it, and makes the check consitent
in behaviour.

(cherry picked from commit 64e9cf00)

(cherry picked from commit baa671a3)