Importing a URL that was created on a different target

[samelhusseini]

Importing a URL that's created on a different target yields a silent crash while attempting to load the project.

We should let the user know that this is the wrong target for the project they're trying to import.

Repro steps:

• Go to arcade.makecode.com
• Import from URL
• Paste in this URl: https://makecode.com/_PCWEutUcRUPT (which was created on pxt-microbit).

See the editor attempt to load it, and then silently fail with a crash in the console.

[ChaseMor]

Is the crashing because a URL from another editor is being used or because importing projects via a URL is currently broken as described in microsoft/pxt-arcade#342?

[samelhusseini]

Importing from a URL that was created by a different target through normal importing of urls not through extensions..