Qualify a couple local constexpr values as 'static' to allow use from within non-capturing lambdas
Qualify a couple local constexpr values as 'static' to allow use from within non-capturing lambdas

Summary: MSVC doesn't allow non-static locals to be accessed within a non-capturing lambda, and some were introduced into the json code.

Reviewed By: yfeldblum

Differential Revision: D4856242

fbshipit-source-id: b2db36ca37a79a41237d39cc7e7b839a5416922f

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