Switch all icons to be defined with private use codepoints instead of ASCII letters

client/scss/settings/_variables.icons.scss

@@ -1,88 +1,87 @@
 $icons: (
-    'cogs': 'a',
-    'doc-empty-inverse': 'b',
-    'doc-empty': 'c',
-    'edit': 'd',
-    'arrow-up': 'e',
-    'arrow-down': 'q',
-    'search': 'f',
-    'cross': 'g',
-    'folder-open-1': 'i',
-    'folder-inverse': 'j',
-    'mail': 'k',
-    'arrows-up-down': 'l',
-    'locked': 'm',
-    'arrow-right': 'n',
-    'doc-full': 'h',
-    'file-text-alt': 'h',
-    'image': 'o',
-    'picture': 'o',
-    'unlocked': 'p',
-    'doc-full-inverse': 'r',
-    'folder': 's',
-    'plus': 't',
-    'tag': 'u',
-    'folder-open-inverse': 'v',
-    'cog': 'w',
-    'tick': 'x',
-    'user': 'y',
-    'arrow-left': 'z',
-    'tick-inverse': 'A',
-    'plus-inverse': 'B',
-    'snippet': 'D',
-    'wagtail': 'V',
-    'wagtail-inverse': '0',
-    'bold': 'C',
-    'italic': 'E',
-    'undo': 'H',
-    'repeat': 'I',
-    'list-ol': 'G',
-    'list-ul': 'F',
-    'link': 'J',
-    'radio-full': 'K',
-    'radio-empty': 'L',
-    'arrow-up-big': 'M',
-    'arrow-down-big': 'N',
-    'group': 'O',
-    'media': 'P',
-    'password': 'Q',
-    'download': 'S',
-    'order': 'T',
-    'grip': 'U',
-    'home': 'W',
-    'order-down': 'X',
-    'order-up': 'Y',
-    'bin': 'Z',
-    'spinner': '1',
-    'pick': '2',
-    'redirect': '3',
-    'view': '4',
-    'no-view': '^',
-    'collapse-down': '5',
-    'collapse-up': '6',
-    'date': '7',
-    'time': '8',
-    'success': '9',
-    'help': '?',
-    'warning': '!',
-    'form': '$',
-    'site': '@',
-    'placeholder': '{',
-    'pilcrow': '\e600',
-    'title': '\f034',
-    'code': '\e601',
-    'openquote': '“',
+    'arrow-down-big': '\e030',
+    'arrow-down': '\e01a',
+    'arrow-left': '\e022',
+    'arrow-right': '\e017',
+    'arrow-up-big': '\e02f',
+    'arrow-up': '\e010',
+    'arrows-up-down': '\e016',
+    'bin': '\e038',
+    'bold': '\e026',
+    'chain-broken': '\e047',
+    'code': '\e001',
+    'cog': '\e020',
+    'cogs': '\e00c',
+    'collapse-down': '\e03f',
+    'collapse-up': '\e03e',
+    'cross': '\e012',
+    'date': '\e045',
+    'doc-empty-inverse': '\e00d',
+    'doc-empty': '\e00e',
+    'doc-full-inverse': '\e01b',
+    'doc-full': '\e018',
+    'download': '\e044',
+    'edit': '\e00f',
+    'folder-inverse': '\e014',
+    'folder-open-1': '\e013',
+    'folder-open-inverse': '\e01f',
+    'folder': '\e01c',
+    'form': '\e00b',
+    'grip': '\e03b',
+    'group': '\e031',
+    'help': '\e041',
+    'home': '\e035',
+    // horizontalrule is not rendered as an icon font – it uses a unicode dash character rendered with a fallback font.
     'horizontalrule': '\2014',
-    'chain-broken': '\e900',
-    'table': '\f0ce',
-    'logout': '\e901',
-    'superscript': '\f12b',
-    'subscript': '\f12c',
-    'strikethrough': '\f0cc'
+    'image': '\e019',
+    'italic': '\e027',
+    'link': '\e02c',
+    'list-ol': '\e029',
+    'list-ul': '\e028',
+    'locked': '\e009',
+    'logout': '\e049',
+    'mail': '\e015',
+    'media': '\e032',
+    'no-view': '\e006',
+    'openquote': '\e000',
+    'order-down': '\e036',
+    'order-up': '\e037',
+    'order': '\e034',
+    'password': '\e033',
+    'pick': '\e03d',
+    'pilcrow': '\e002',
+    'placeholder': '\e003',
+    'plus-inverse': '\e024',
+    'plus': '\e01d',
+    'radio-empty': '\e02e',
+    'radio-full': '\e02d',
+    'redirect': '\e03c',
+    'repeat': '\e02b',
+    'search': '\e011',
+    'site': '\e007',
+    'snippet': '\e025',
+    'spinner': '\e03a',
+    'strikethrough': '\e04a',
+    'subscript': '\e04c',
+    'success': '\e043',
+    'superscript': '\e04b',
+    'table': '\e048',
+    'tag': '\e01e',
+    'tick-inverse': '\e023',
+    'tick': '\e021',
+    'time': '\e008',
+    'title': '\e046',
+    'undo': '\e02a',
+    'unlocked': '\e00a',
+    'user': '\e004',
+    'view': '\e005',
+    'wagtail-inverse': '\e040',
+    'wagtail': '\e039',
+    'warning': '\e042',
 );
 
 $icons-after: (
-    'arrow-down-after': 'q',
-    'arrow-up-after': 'e',
-    'arrow-right-after': 'n'
+    'arrow-down-after': map-get($icons, 'arrow-down'),
+    'arrow-right-after': map-get($icons, 'arrow-right'),
+    'arrow-up-after': map-get($icons, 'arrow-up'),
 );