`Char.fromCode` throws a `RangeError` out of range, but its documentation says it returns U+FFFD

[gilramir]

Found against: gren 0.6.6, gren-lang/core 7.4.2, node 2

Summary

Char.fromCode : Int -> Char's doc comment says what a number outside Unicode's
range of codepoints returns:

The full range of unicode is from 0 to 0x10FFFF. With numbers outside that
range, you get [the replacement character][fffd].

with fromCode -1 == '�' as its own example. It throws instead:
_Char_fromCode is __Utils_chr(String.fromCodePoint(code)), and
String.fromCodePoint raises a RangeError below 0 and above 0x10FFFF.

The documentation is accurate about Elm, which the module was derived from —
elm/core's kernel guards the range and returns U+FFFD — and Gren's rewrite to
String.fromCodePoint dropped the guard along with the surrogate arithmetic it
replaced. Nothing in the doc comment was changed, so the two have disagreed
since.

Reproduction

> Char.fromCode 65
'A' : Char
> Char.toCode (Char.fromCode 0xD800)
55296 : Int
> Char.fromCode -1
RangeError: Invalid code point -1
> Char.fromCode 0x110000
RangeError: Invalid code point 1114112

expression	documented	actual
Char.fromCode 65	'A'	'A'
Char.fromCode 0xD800	not mentioned	a Char holding a lone surrogate
Char.fromCode -1	'\u{FFFD}'	RangeError: Invalid code point -1
Char.fromCode 0x110000	'\u{FFFD}'	RangeError: Invalid code point 1114112

[robinheghan]

fixed on release branch