Feature: Support auto-complete in debug console

[znorman-harris]

We are missing the "supportsCompletionsRequest" from our capabilities and need to add that method.

Because this is a feature that really should live on the language server, we are going to need a message protocol to send and receive a response for this (or see if this might be something that is already in the API for the language server).

But, this is an important detail missing when running IDL.

[znorman-harris]

Make sure we also consider local variables when using auto-complete, based on the scope.