Adopt EnvironmentVariableCollection.description

[Tyriar]

There's a new API (microsoft/vscode#171108) being finalized this month that allows extensions to explain why it's changing environment variables. Adopting this will show additional information when hovering a terminal tab

API:

https://github.com/microsoft/vscode/blob/e6936ce0ab10bc9fb3ec220db3c4304bdd909292/src/vscode-dts/vscode.proposed.envCollectionWorkspace.d.ts#L27-L33

Current:

After description:

cc @karrtikr

[karrtikr]

Was this verified?

[connor4312]

It was not marked as a feature/bug, though Daniel tested it out (and found microsoft/vscode#186859)

[Tyriar]

Also: microsoft/vscode#186798