@actions/core - provide way to get env context

[timharris777]

Currently the only way to get env vars from the workflow's env context is to use process.env. The issue with this is that process.env also contains tons of system env vars from the host. Please provide a way to for us to access the workflow env context without all the extra host system variables mixed in.

[ohookins]

Additionally, the vars context should also be available to be queried.