Let a button carry a chosen icon before or after its text, and pick icons from tiles

Schema v25: a button takes an optional icon (any name from the shared set or
"none") and an icon position (start or end). Without a choice it keeps the
diagonal arrow behind the text, still with the button-arrow class, so stored
pages and their own CSS look exactly as before.

Thirteen everyday icons join the set (arrow down, chevron, calendar, message,
send, download, document, play, search, heart, info, plus, person). Button,
icon and icon card choose from a tile picker with a drawing per icon, grouped,
keyboard navigable, instead of a select with English keys. icons.js holds the
paths for the editor; a test keeps them equal to the Twig drawings and the
validator list. ADR 108.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

templates/blocks/block.html.twig

@@ -26,7 +26,13 @@
     {% endif %}
 {% elseif type == 'button' %}
     {% for device, settings in layout.button|default({}) %}{% for key, value in settings %}{% set designClasses = designClasses ~ ' b-' ~ device ~ '-' ~ key ~ '-' ~ value %}{% endfor %}{% endfor %}
-    <a id="{{ block.id }}" class="button cms-button{{ designClasses }}" href="{{ props.href }}"{% include 'blocks/link-attributes.html.twig' with {newTab: props.newTab|default(false)} only %}>{{ props.text }} <span class="button-arrow" aria-hidden="true">{% include 'blocks/icon.html.twig' with {name: 'arrow-up-right'} only %}</span></a>
+    {# Schema v25: Symbol wählbar. Ohne Angabe der Pfeil wie bisher; er behält die Klasse
+       button-arrow, damit eigenes CSS älterer Websites (ausblenden, drehen) weiter greift. #}
+    {% set buttonIcon = props.icon|default('arrow-up-right') %}
+    {% set iconMarkup = '' %}
+    {% if buttonIcon != 'none' %}{% set iconMarkup %}<span class="button-icon{{ buttonIcon == 'arrow-up-right' ? ' button-arrow' }}" aria-hidden="true">{% include 'blocks/icon.html.twig' with {name: buttonIcon} only %}</span>{% endset %}{% endif %}
+    {% set iconFirst = props.iconPosition|default('end') == 'start' %}
+    <a id="{{ block.id }}" class="button cms-button{{ designClasses }}" href="{{ props.href }}"{% include 'blocks/link-attributes.html.twig' with {newTab: props.newTab|default(false)} only %}>{% if iconMarkup and iconFirst %}{{ iconMarkup }} {% endif %}{{ props.text }}{% if iconMarkup and not iconFirst %} {{ iconMarkup }}{% endif %}</a>
 {% elseif type == 'image' %}
     {# Wie breit das Bild tatsaechlich erscheint. Steht im Block eine feste Breite - ein Logo mit
        190px, ein Symbol mit 72px -, dann ist das die Antwort, und der Browser laedt die kleine