Add prompt to make Stirling your default PDF app (#4890)

# Description of Changes
- Adds a reusable banner component/system to the core app
- Adds banner at the top of the desktop app if Stirling isn't your
default PDF editor, with a button to make it your default
- Adds a permanent button in the settings to do it manually (in case
you've dismissed the banner)
- Simplifies the file loading logic to fix a bug where the input file
could be duplicated occasionally. Now, the TS just receives files from
one buffer, regardless of how they've been passed to the app in Rust.

## Caveats
I've only been able to get the setting of default apps working properly
on Mac. The Windows build isn't signed (yet) so we can't use the proper
API for it, so currently it just sends you to the Settings UI. I've also
not been able to test it on Linux at all.

frontend/public/locales/en-GB/translation.json

@@ -41,6 +41,30 @@
     "cancel": "Cancel",
     "confirm": "Extract"
   },
+  "defaultApp": {
+    "title": "Set as Default PDF App",
+    "message": "Would you like to set Stirling PDF as your default PDF editor?",
+    "description": "You can change this later in your system settings.",
+    "notNow": "Not Now",
+    "setDefault": "Set Default",
+    "dismiss": "Dismiss",
+    "prompt": {
+      "title": "Set as Default PDF Editor",
+      "message": "Make Stirling PDF your default application for opening PDF files."
+    },
+    "success": {
+      "title": "Default App Set",
+      "message": "Stirling PDF is now your default PDF editor"
+    },
+    "settingsOpened": {
+      "title": "Settings Opened",
+      "message": "Please select Stirling PDF in your system settings"
+    },
+    "error": {
+      "title": "Error",
+      "message": "Failed to set default PDF handler"
+    }
+  },
   "language": {
     "direction": "ltr"
   },
@@ -332,7 +356,13 @@
       "mode": {
         "fullscreen": "Fullscreen",
         "sidebar": "Sidebar"
-      }
+      },
+      "defaultPdfEditor": "Default PDF editor",
+      "defaultPdfEditorActive": "Stirling PDF is your default PDF editor",
+      "defaultPdfEditorInactive": "Another application is set as default",
+      "defaultPdfEditorChecking": "Checking...",
+      "defaultPdfEditorSet": "Already Default",
+      "setAsDefault": "Set as Default"
     },
     "hotkeys": {
       "title": "Keyboard Shortcuts",