chore(web): improve reporting on dictionary load errors

[mcdurdin]

Some error messages do not include the URL, so it can be hard to disambiguate them. Will not back-port to 18.0, because the errors are currently rare.

See, for example: https://keyman.sentry.io/issues/6580990108/events/6493a8ffede448029c1a97ab828b029e/

See-also: #16628
Test-bot: skip

[keymanapp-test-bot]

User Test Results

Test specification and instructions

User tests are not required

Test Artifacts

• Android (no artifacts on BuildLevel "build")
  • Keyman for Android apk - build : ✅ all tests passed
  • FirstVoices Keyboards for Android apk - build : ✅ all tests passed
  • KeyboardHarness apk - build : ✅ all tests passed
  • KMSample1 apk - build : ✅ all tests passed
  • KMSample2 apk - build : ✅ all tests passed
• Developer (no artifacts on BuildLevel "build")
  • Keyman Developer - build : ✅ all tests passed
  • Compiler Regression Tests - build : ✅ all tests passed
  • kmcomp.zip - build : ✅ all tests passed
• iOS (no artifacts on BuildLevel "build")
  • Keyman for iOS (simulator image) - build : ✅ all tests passed
  • FirstVoices Keyboards for iOS (simulator image) - build : ✅ all tests passed
• Keyboards (no artifacts on BuildLevel "build")
  • Test Keyboards - build : ✅ all tests passed
• Web (no artifacts on BuildLevel "build")
  • KeymanWeb Test Home - build : ✅ all tests passed

[keyman-server]

Changes in this pull request will be available for download in Keyman version 19.0.292-alpha