Add a small margin between the border of media and "Hide Media" button

I thought we had this already, I don't know where it went, but now it's
back.

src/messagecontent/ImageComponent.qml

@@ -49,6 +49,7 @@ Item {
     QQC2.Button {
         anchors.right: parent.right
         anchors.top: parent.top
+        anchors.margins: Kirigami.Units.smallSpacing
         visible: !_private.hideImage
         icon.name: "view-hidden"
         text: i18nc("@action:button", "Hide Image")

src/messagecontent/VideoComponent.qml

@@ -177,6 +177,7 @@ Video {
     QQC2.Button {
         anchors.right: parent.right
         anchors.top: parent.top
+        anchors.margins: Kirigami.Units.smallSpacing
         visible: root.state !== "hidden"
         icon.name: "view-hidden"
         text: i18nc("@action:button", "Hide Image")