Add support for the "accept" attribute on file inputs.

If the widget's field - if there is one - has the "accept" attribute set (the
`NamedImage` field has `image/*` set by default) then this is rendered as an
`accept` attribute on the file input.

This would restrict the allowed file types before uploading while still being
checked on the server side.

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

news/198.feature

@@ -0,0 +1,14 @@
+Add support for the "accept" attribute on file inputs.
+
+If the widget's field - if there is one - has the "accept" attribute set (the
+`NamedImage` field has `image/*` set by default) then this is rendered as an
+`accept` attribute on the file input.
+
+This would restrict the allowed file types before uploading while still being
+checked on the server side.
+
+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
+[thet]

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;