Remove moment as a dependency for apollo-language-server

[nickpith]

There is really no strong need for moment to a dependency of apollo-language-server when it is used just to calculate durations in milliseconds. A simple constant will suffice instead.

Also added some tests to prove that this change works but is by no means exhaustive.

Related: #2323.

TODO:

• Update CHANGELOG.md* with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

*Make sure changelog entries note which project(s) has been affected. See older entries for examples on what this looks like.

[apollo-cla]

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[trevor-scheer]

Thanks @nickpith! I updated your PR description so it doesn't autoclose the related issue. We still need to remove moment in the CLI itself in order to close that one out (even though the author of that issue wrote in that it's due to the usage in apollo-language-server).

As mentioned in #2593, I'll make a best effort w.r.t. this repo and try to get a release of this cut in a reasonable time, but my current focus is AS4. Apologies for any inconvenience this causes in the meantime.

[nickpith]

@trevor-scheer Thanks for merging and fixing the description. I can understand the focus on AS4 so whenever you can get to it would be fine!