Add methods to iterate exemplar characters

[lionel-rowe]

Adds public code_point_ranges and strings methods to ExemplarCharacters to allow iterating through the single- and multi-character entries, respectively:

• code_point_ranges returns a CodePointRangeIterator (existing struct)
• strings returns a StringIterator, a new struct that iterates via passing a DiplomatWrite buffer to its next method, writing a null-char-terminated string for Some(string) and an empty string for None (thus differentiating Some("") -> "\0" from None -> "", though in practice Some("") should never occur for exemplar chars). Not sure if there's a better way of iterating strings across the FFI boundary.

Thus for hu locale and Main set:

# `code_point_ranges`
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'r', 's', 't', 'u', 'v', 'z', 'á', 'é', 'í', 'ó', 'ö', 'ú', 'ü', 'ő', 'ű'
# `strings`
"ccs", "cs", "ddz", "ddzs", "dz", "dzs", "ggy", "gy", "lly", "ly", "nny", "ny", "ssz", "sz", "tty", "ty", "zs", "zzs"

I also added a tab to the WASM demo to illustrate how these can be used from JS/TS.

[sffc]

Hi @lionel-rowe, do you plan to address @Manishearth's feedback?

[lionel-rowe]

@sffc Sorry for delayed reply, I had a go at fixing the issues but TBH my Rust knowledge is lacking. I might have another crack at it later but not sure when I'll have time.

[CLAassistant]

All committers have signed the CLA.

[Manishearth]

Ignore the CLA assistant if you already signed it. It's buggy right now, we'll let you know when you can sign if you haven't signed already

[sffc]

Ignore the CLA assistant if you already signed it. It's buggy right now, we'll let you know when you can sign if you haven't signed already

Fixed