fix(core): add tabIndex=0 to FieldActionMenu so that webkit can tab t…

…o it like other browsers

Chromium and Firefox will tab to the FieldActions menu without tabIndex=0,
but Webkit needs to have it explicitly set in order to include it in the tab flow

packages/sanity/src/core/form/field/actions/FieldActionMenu.tsx

@@ -137,6 +137,7 @@ function RootFieldActionMenuGroup(props: {
     <MenuButton
       button={
         <Button
+          tabIndex={0}
           icon={node.icon}
           aria-label={open ? undefined : title}
           data-testid="field-actions-trigger"