Initially load option at newIndex and remaining options on focus

Optimization for big notetypes:
Should increase efficiency from O(n²) to O(n). Test on notetype with 500 templates shows significant improvement in load time (~10s down to ~1s).

ts/change-notetype/MapperRow.svelte

@@ -21,29 +21,34 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
         current = oldNames[newIndex] || tr.changeNotetypeNothing();
     }
 
-    function onChange(evt: Event) {
-        const oldIdx = parseInt((evt.target as HTMLSelectElement).value, 10);
-        state.setOldIndex(ctx, newIndex, oldIdx);
-    }
-
     // optimization for big notetypes
     let active: boolean = false;
     function activate(evt: Event) {
         active = true;
     }
+
+    function onChange(evt: Event) {
+        const oldIdx = parseInt((evt.target as HTMLSelectElement).value, 10);
+        state.setOldIndex(ctx, newIndex, oldIdx);
+    }
 </script>
 
 <Row --cols={2}>
     <Col --col-size={1}>
         <!-- svelte-ignore a11y-no-onchange -->
         <select
-            value={$info.getOldIndex(ctx, newIndex)}
+            value={active ? $info.getOldIndex(ctx, newIndex) : 0}
             class="form-select"
+            on:focusin={activate}
             on:change={onChange}
         >
-            {#each $info.getOldNamesIncludingNothing(ctx) as name, idx}
+            {#if active}
+                {#each oldNames as name, idx}
                     <option value={idx}>{name}</option>
                 {/each}
+            {:else}
+                <option value={0}>{current}</option>
+            {/if}
         </select>
     </Col>
     <Col --col-size={1}>