Merge "Loading NW.js" and "Loading Electron" strings

Translators do not need to worry about what these are
There will probably be even more in the future

src/locales/en.json

@@ -56,8 +56,9 @@
     "packagingProject": {
       "string": "Packaging project"
     },
-    "loadingNwjs": {
-      "string": "Loading NW.js"
+    "loadingLargeAsset": {
+      "string": "Loading {thing}",
+      "context": "Generic loading message used when loading a \"brand name\" file such as NW.js or Electron."
     },
     "loadingScripts": {
       "string": "Loading scripts"

src/packager/PackagerOptions.svelte

@@ -60,9 +60,9 @@
 
   const handleLargeAssetFetchProgress = ({detail}) => {
     if (detail.asset.startsWith('nwjs-')) {
-      $progress.text = $_('progress.loadingNwjs');
+      $progress.text = $_('progress.loadingLargeAsset').replace('{thing}', 'NW.js');
     } else if (detail.asset.startsWith('electron-')) {
-      $progress.text = 'Loading Electron';
+      $progress.text = $_('progress.loadingLargeAsset').replace('{thing}', 'Electron');
     }
     $progress.progress = detail.progress;
   };