EuiComboBox with no custom option: bug fix, cleaned up example, added comment

[chandlerprall]

Summary

Resolves #1790

Fixed a bug in determining when the focus had left EuiComboBox and added a form row with error to the Disallowing custom options example explaining to the user why the field is marked invalid.

Checklist

- [ ] This was checked in mobile
- [ ] This was checked in IE11
- [ ] This was checked in dark mode
- [ ] Any props added have proper autodocs
- [ ] Documentation examples were added

• A changelog entry exists and is marked appropriately
• This was checked for breaking changes and labeled appropriately
  - [ ] Jest tests were updated or added to match the most common scenarios
  - [ ] This was checked against keyboard-only and screenreader scenarios
  - [ ] This required updates to Framer X components

[cjcenizal]

Tested locally, code LGTM! Thanks for fixing this. Had a couple minor suggestions.

[cchaos]

My only concern is that when you tab back into it (Shift + tab), while the input stays in an invalid state the help text is gone.

[chandlerprall]

@cchaos updated to clear the error state only when the options change, or the field is re-blurred + the input is empty

[cchaos]

Hey, sorry one more case where if you close the dropdown via tabbing and selecting the arrow, the error message doesn't change correctly.

[chandlerprall]

@cchaos @cjcenizal updated to have two validation paths: first is the existing onBlur, second is when the value changes, it checks to see if there are any matching options.

I found a separate issue, when the input has an exact match but additional partial match(es), the wording is incorrect:

titan is valid but still not selected. I think the onBlur text should be updated to something like "titan" was not saved but I can't come up with exact wording that I like.

[cchaos]

I'm good with how it's working now. The only possibly odd thing is using the dropdown arrow will show the error message but it won't change the state of the input until you click outside of it.

But, I can probably live with that? The only worry would be if the consumer doesn't provide an error message. So maybe I'm back-tracking and that should be fixed as well?

but I can't come up with exact wording that I like

I'd just leave the error message as it is. It's only the docs anyway

[cjcenizal]

LGTM! Great work.

[chandlerprall]

@cchaos updated to also indicate invalid state when the dropdown arrow is clicked