tools: add BigInt to globals
I was going to do it in https://github.com/nodejs/node/pull/19691, but then I noticed that https://github.com/nodejs/node/pull/20220 added several // eslint-disable-next-line no-undef
lines. I talked about it with @ljharb and we agreed that a separate PR makes more sense.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
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