Add support for accept attribute on file input.

If the widget's field - if there is one - has `allowedContentTypes` set (the `NamedImage` field has `image/*` set by default) the allowed content types are rendered as `accept` attribute on the file input.

This already restricts the allowed file types before uploading while still being checked on the server side too.

Fixes: plone/plone.formwidget.namedfile#66
Depends on:
- plone/plone.namedfile#158
- plone/plone.formwidget.namedfile#67

news/198.feature

@@ -0,0 +1,10 @@
+Add support for accept attribute on file input.
+
+If the widget's field - if there is one - has `allowedContentTypes` set (the `NamedImage` field has `image/*` set by default) the allowed content types are rendered as `accept` attribute on the file input.
+
+This already restricts the allowed file types before uploading while still being checked on the server side too.
+
+Fixes: https://github.com/plone/plone.formwidget.namedfile/issues/66
+Depends on:
+- https://github.com/plone/plone.namedfile/pull/158
+- https://github.com/plone/plone.formwidget.namedfile/pull/67

plone/app/z3cform/templates/file_input.pt

@@ -133,6 +133,7 @@
   </tal:block>
 
   <input class="form-control"
+         accept="${view/accept}"
          type="file"
          tal:define="
            is_invalid python:view.error and 'is-invalid' or '';

plone/app/z3cform/templates/image_input.pt

@@ -139,6 +139,7 @@
   </tal:block>
 
   <input class="form-control"
+         accept="${view/accept}"
          type="file"
          tal:attributes="
            id string:${view/id}-input;