Add "option" to list elements that belong to "listbox"

The accessibility attribute `role="listbox"` requires its immediate children to be set as `role="option"`, currently they don't have this option and accessibility tests are failing.

src/Forms/CheckboxSetField.php

@@ -90,6 +90,7 @@ class CheckboxSetField extends MultiSelectField
             $options->push(new ArrayData(array(
                 'ID' => $itemID,
                 'Class' => $extraClass,
+                'Role' => 'option',
                 'Name' => "{$this->name}[{$itemValue}]",
                 'Value' => $itemValue,
                 'Title' => $title,

src/Forms/OptionsetField.php

@@ -72,6 +72,7 @@ class OptionsetField extends SingleSelectField
         return new ArrayData(array(
             'ID' => $this->getOptionID($value),
             'Class' => $this->getOptionClass($value, $odd),
+            'Role' => 'option',
             'Name' => $this->getOptionName(),
             'Value' => $value,
             'Title' => $title,

templates/SilverStripe/Forms/CheckboxSetField.ss

@@ -1,7 +1,7 @@
 <ul $AttributesHTML>
 	<% if $Options.Count %>
 		<% loop $Options %>
-			<li class="$Class">
+			<li class="$Class" role="$Role">
 				<input id="$ID" class="checkbox" name="$Name" type="checkbox" value="$Value.ATT"<% if $isChecked %> checked="checked"<% end_if %><% if $isDisabled %> disabled="disabled"<% end_if %> />
 				<label for="$ID">$Title</label>
 			</li>

templates/SilverStripe/Forms/OptionsetField.ss

@@ -1,6 +1,6 @@
 <ul $AttributesHTML>
 	<% loop $Options %>
-		<li class="$Class">
+		<li class="$Class" role="$Role">
 			<input id="$ID" class="radio" name="$Name" type="radio" value="$Value"<% if $isChecked %> checked<% end_if %><% if $isDisabled %> disabled<% end_if %> <% if $Up.Required %>required<% end_if %> />
 			<label for="$ID">$Title</label>
 		</li>