Add tooltip to mask editor button

ftl/core/editing.ftl

@@ -92,8 +92,8 @@ editing-image-occlusion-rectangle-tool = Rectangle
 editing-image-occlusion-ellipse-tool = Ellipse
 editing-image-occlusion-polygon-tool = Polygon
 editing-image-occlusion-text-tool = Text
+editing-image-occlusion-toggle-mask-editor = Toggle Mask Editor
  
-
 ## You don't need to translate these strings, as they will be replaced with different ones soon.
 
 editing-html-editor = HTML Editor

ts/editor/editor-toolbar/ImageOcclusionButton.svelte

@@ -3,6 +3,7 @@ Copyright: Ankitects Pty Ltd and contributors
 License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 -->
 <script lang="ts">
+    import * as tr from "@tslib/ftl";
     import ButtonGroup from "components/ButtonGroup.svelte";
     import DynamicallySlottable from "components/DynamicallySlottable.svelte";
     import IconButton from "components/IconButton.svelte";
@@ -33,6 +34,7 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
                 on:click={() => {
                     $ioMaskEditorVisible = !$ioMaskEditorVisible;
                 }}
+                tooltip={tr.editingImageOcclusionToggleMaskEditor()}
             >
                 {@html mdiViewDashboard}
             </IconButton>