Unable to set custom icon for block:

1. create new custom block:

ezplatform_page_fieldtype:
    blocks:
        hero:
            name: Hero
            category: default
            thumbnail: 'assets/images/page_builder/blocks/hero.svg'
            views:
                default: { name: 'Default block layout', template: '@ezdesign/blocks/hero.html.twig' }
            attributes:
                text:
                    name: Content
                    type: text
                    validators:
                        not_blank:
                            message: You must provide a text
                        regexp:
                            options:
                                pattern: '/[^\\s]/'
                            message: Only valid HTML code is allowed
                image:
                    name: Image
                    type: embed
                    validators:
                        not_blank:
                            message: You must provide value
                        regexp:
                            options:
                                pattern: '/[0-9]+/'
                            message: Choose a Content item

2. goto edit mode in page builder

expected behaviour: icon should be loaded from `/bundles/ezplatformadminui/img/ez-icons.svg#block_name`:

assets/images/page_builder/blocks/hero.svg

current behaviour: icon is loaded from

<svg class="ez-icon"><use xlink:href="/bundles/ezplatformadminui/img/ez-icons.svg#hero"></use></svg>