feature #26502 [Form] Add Bootstrap 4 style for field FileType (zenmate)

This PR was squashed before being merged into the 4.1-dev branch (closes #26502).

Discussion
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[Form] Add Bootstrap 4 style for field FileType

| Q             | A
| ------------- | ---
| Branch?       | master<!-- see below -->
| Bug fix?      | no
| New feature?  | yes <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #26464   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

<!--
Write a short README entry for your feature/bugfix here (replace this comment block.)
This will help people understand your PR and can be used as a start of the Doc PR.
Additionally:
 - Bug fixes must be submitted against the lowest branch where they apply
   (lowest branches are regularly merged to upper ones so they get the fixes too).
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Commits
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df57718 [Form] Add Bootstrap 4 style for field FileType

src/Symfony/Bridge/Twig/Resources/views/Form/bootstrap_4_layout.html.twig

@@ -117,7 +117,7 @@
 
 {% block form_widget_simple -%}
     {% if type is not defined or type != 'hidden' %}
-        {%- set attr = attr|merge({class: (attr.class|default('') ~ ' form-control' ~ (type|default('') == 'file' ? '-file' : ''))|trim}) -%}
+        {%- set attr = attr|merge({class: (attr.class|default('') ~ (type|default('') == 'file' ? ' custom-file-input' : ' form-control'))|trim}) -%}
     {% endif %}
     {%- if type is defined and (type == 'range' or type == 'color') %}
         {# Attribute "required" is not supported #}
@@ -187,6 +187,8 @@
         {%- if compound is defined and compound -%}
             {%- set element = 'legend' -%}
             {%- set label_attr = label_attr|merge({class: (label_attr.class|default('') ~ ' col-form-label')|trim}) -%}
+        {% elseif type is defined and type == 'file' %}
+            {%- set label_attr = label_attr|merge({for: id, class: (label_attr.class|default('') ~ ' custom-file-label')|trim}) -%}
         {%- else -%}
             {%- set label_attr = label_attr|merge({for: id, class: (label_attr.class|default('') ~ ' form-control-label')|trim}) -%}
         {%- endif -%}
@@ -263,6 +265,15 @@
     </{{ element|default('div') }}>
 {%- endblock form_row %}
 
+{% block file_row -%}
+    <div class="form-group">
+        <{{ element|default('div') }} class="custom-file">
+            {{- form_widget(form) -}}
+            {{- form_label(form) -}}
+        </{{ element|default('div') }}>
+    </div>
+{% endblock %}
+
 {# Errors #}
 
 {% block form_errors -%}