Fix username display issues (#6471)

# Description of Changes
Main fixes:
- Fix the display of the username in the bottom left
- Now displays as "User" when not logged in on self-hosted (desktop) and
"Guest" on SaaS when logged in anonymously
- Now updates properly when the user logs in/out in SaaS, desktop and
self-hosted
- Fix incremental build issues in the desktop app that have been here
since the start (I hope at least - I think the issue is that the JLink
is built read-only and then on subsequent builds you get OS errors when
trying to override the JLink with the new version. There's no real need
for it to be read-only that I know of, so we might as well just make it
R/W and ship like that)

frontend/editor/public/locales/en-GB/translation.toml

@@ -1764,6 +1764,10 @@ insufficientPermissions = "You do not have permission to perform this action."
 pleaseLoginAgain = "Please login again."
 sessionExpired = "Session Expired"
 
+[auth.displayName]
+guest = "Guest"
+user = "User"
+
 [auto-rename]
 description = "Automatically finds the title from your PDF content and uses it as the filename."
 header = "Auto Rename PDF"