[BUGFIX beta] fillIn only sets value to first match.

[Serabe]

Currently, fillIn sets the new value to all matches, though the events are
only fired for the first one, making Ember only aware of that one.

This can cause a problem while trying to debug a test.

Fixes #14018

[Serabe]

IMHO, fillIn should raise an error if more than one element matches (like the Capybara::Ambiguous error). I understand that that would be backwards incompatible and would need to wait until 3.0 or to be added to the Grand Testing Unification RFC

[rwjblue]

@Serabe - Good point RE: ambiguous match. Can you comment on the RFC about that so I remember to incorporate it?

[Serabe]

Thank you. Just did!

[rwjblue]

Also, this is good to go once CI passes. Though at some point (hopefully soon) I need to come back and remove the remaining jQuery usage in the acceptance test helper stuff. We switched to native events (which is awesome), but still have some jQueryisms in here to fix.

[rwjblue]

Thanks again @Serabe!