Use fs to import JSON

[ptomato]

Importing JSON doesn't work natively.

Un-pin the version of node.

[codecov]

Codecov Report

Merging #351 into main will increase coverage by 0.61%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #351      +/-   ##
==========================================
+ Coverage   83.39%   84.01%   +0.61%     
==========================================
  Files          17       17              
  Lines        3415     3415              
  Branches      403      384      -19     
==========================================
+ Hits         2848     2869      +21     
+ Misses        536      517      -19     
+ Partials       31       29       -2

Impacted Files	Coverage Δ
polyfill/lib/ecmascript.mjs	93% <0%> (+0.1%)	⬆️
polyfill/lib/timezone.mjs	87.2% <0%> (+0.58%)	⬆️
polyfill/lib/absolute.mjs	88.38% <0%> (+0.64%)	⬆️
polyfill/lib/time.mjs	74.77% <0%> (+0.91%)	⬆️
polyfill/lib/datetime.mjs	81.7% <0%> (+1.21%)	⬆️
polyfill/lib/slots.mjs	89.09% <0%> (+1.81%)	⬆️
polyfill/lib/yearmonth.mjs	77.18% <0%> (+2.01%)	⬆️
polyfill/lib/monthday.mjs	81.2% <0%> (+2.01%)	⬆️
polyfill/lib/date.mjs	72.04% <0%> (+2.48%)	⬆️
polyfill/lib/now.mjs	100% <0%> (+3.33%)	⬆️

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