Add descriptions to Decky titleview DialogButtons (#502)

* chore: add onOKActionDescriptions to decky titleview

This is in preparation for beebles' custom titleview. Since plugins may reuse the same icons in their custom titleviews, it will be a good practice to disambiguate their meanings. In the Steam UI, any icon button has a matching description.

* chore: implement it using the translation framework

---------

Co-authored-by: Marco Rodolfi <marco.rodolfi@tuta.io>

backend/locales/en-US.json

@@ -234,6 +234,10 @@
       "testing": "Testing"
     }
   },
+  "TitleView":{
+    "decky_store_desc": "Open Decky Store",
+    "settings_desc": "Open Decky Settings"
+  },
   "Updater": {
     "decky_updates": "Decky Updates",
     "no_patch_notes_desc": "no patch notes for this version",