Specify & implement JSON representation for Temporal.Calendar as identifier

[cjtenny]

Allows Calendar serialization to JSON.

Fixes #1227 separate from #1245

[codecov]

Codecov Report

Merging #1273 (62884ec) into main (5930868) will increase coverage by 2.25%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1273      +/-   ##
==========================================
+ Coverage   93.55%   95.81%   +2.25%     
==========================================
  Files          19       19              
  Lines        7961     9367    +1406     
  Branches     1264     1437     +173     
==========================================
+ Hits         7448     8975    +1527     
+ Misses        506      386     -120     
+ Partials        7        6       -1     

Flag	Coverage Δ
test262	55.95% <ø> (+14.34%)	⬆️
tests	91.98% <ø> (+2.54%)	⬆️

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Impacted Files	Coverage Δ
polyfill/lib/shim.mjs
polyfill/lib/legacydate.mjs
polyfill/lib/intrinsicclass.mjs
polyfill/lib/slots.mjs
lib/intrinsicclass.mjs	59.09% <0.00%> (ø)
lib/plainyearmonth.mjs	95.52% <0.00%> (ø)
lib/zoneddatetime.mjs	97.80% <0.00%> (ø)
lib/legacydate.mjs	0.00% <0.00%> (ø)
lib/now.mjs	100.00% <0.00%> (ø)
lib/plainmonthday.mjs	91.32% <0.00%> (ø)
... and 13 more

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[ptomato]

👍, the example code in the documentation is a bit contrived as we discussed on chat, but it's something we can fix later 😄