Update the ISO-8859 encodings to match the current standards

[brianquinlan]

• Update the ISO-8859-* encodings to match the current standards at https://unicode.org/Public/MAPPINGS

I generated the mappings using this script:

import unicodedata

top_controls = (r'\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c'
    r'\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e'
    r'\x9f\xa0')

def get_char_mapping(encoding, r=None):
    s = ""
    if r is None:
        r = range(256)
    for i in r:
        try:
            ch = bytes([i]).decode(encoding)
        except UnicodeDecodeError:
            s += '\\ufffd'
        else:
            if ord(ch) > 0xffff:
                raise ValueError('not in BMP')
            if unicodedata.category(ch).startswith('C') or unicodedata.category(ch).startswith('Z'):
                if ord(ch) < 256:
                    s += f'\\x{ord(ch):02x}'
                else:
                    s += f'\\u{ord(ch):04x}'
            else:
                s += ch
    return s

char_map = get_char_mapping('iso8859-3', range(128, 256))
print(char_map.replace(top_controls, '$_topIsoControls'))

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[lrhn]

Use ''' instead of """, to (better) match the other '-quoted strings.

[lrhn]

Not just "new", update to actually use the official Unicode mappings, which we didn't before.
(Mainly because I was not aware they existed, and based these tables directly on the ISO standards.)
So, suggested phrasing

- Update the ISO-8859 mappings to use the Unicode
  consortium's recommended mappings between Unicode
  text and one-byte encodings.

[lrhn]

There should be room for 16 hex-escapes per line (64 chars + start/end quote and indent, easily within 70 chars),
so split in multiples of 16, for ease of reading:

const _top8859controls =
  '\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f'
  '\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f'
  '\xa0';

[lrhn]

Let's do the rest too.
(I'd write a script to fetch and parse the Unicode tables, rather than doing it manually.)

... OK, so I did that.
#93

[mosuem]

Closing as the dart-lang/convert repository is merged into the dart-lang/core monorepo. Please re-open this PR there!