Load JSON at runtime

[MSP-Greg]

Description

Fixes loading JSON when Gemfile contains JSON versions that differ from the default gem or previously loaded versions. Various versions of Bundler have had issues with default gems, as it also loads some of them.

This PR changes JSON loading to runtime.

Closes #2206

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[ylecuyer]

It is working with my reproduction example ;)

I have mixed feelings about this PR as it fixes the issue but isn't really future proof

[MSP-Greg]

but isn't really future proof

In what sense? Loading/requiring at runtime is essentially the same as autoload.

[ylecuyer]

What I meant was if someone in a future commit adds a require 'json' on top of a new file we won't notice it until it breaks again

[MSP-Greg]

Given the possible issues with default gems, I think it would be worthwhile to autoload json, psych/yaml, and openssl. Using autoload removes the need for adding multiple requires when loading at runtime.

I'll have a look at all three.

[nateberkopec]

I'm gonna roll with this for now, we can do a longterm fix later.