Case-normalisation and/or canonicalisation for Calendar identifiers?

[anba]

From #1502

12.1.2 IsBuiltinCalendar ( id )
Should calendar ids be case-normalised? For example time zones names are case-normalised and UTS-35 also ignores casing.

Calendar identifiers are currently neither case-normalised nor canonicalised. For example "ISO8601" is currently spec'ed to throw an error:

js> new Temporal.Calendar("ISO8601")
typein:1:1 RangeError: invalid calendar: ISO8601
Stack:
  @typein:1:1

Time zone identifiers are both case-normalised and canonicalised:

js> new Temporal.TimeZone("EuRoPe/lonDON").id
"Europe/London"
js> new Temporal.TimeZone("Japan").id 
"Asia/Tokyo"

And ECMA-402 also applies case-normalisation and canonicalisation for calendars:

js> new Intl.DateTimeFormat("en", {calendar: "GrEgOrY"}).resolvedOptions().calendar 
"gregory"
js> new Intl.DateTimeFormat("en", {calendar: "islamicc"}).resolvedOptions().calendar 
"islamic-civil"

[ptomato]

I'm trying to get this solved over at tc39/proposal-intl-enumeration#37.

[ptomato]

The case-sensitivity will be fixed by #2395 although I still intend to pursue the proposal-intl-enumeration issue.

[ptomato]

The proposal-intl-enumeration issue was rejected, so I'll pursue that as an editorial ECMA-402 pull request once proposal-intl-enumeration reaches stage 4. With #2395 closed, I think that's the only remaining work to be done, and it's independent of Temporal.