Update error message on "Unwanted U+FEFF" found in *.csv files

[howard-e]

Preview Tests

An error message was being thrown when running npm run build which read:

Unwanted U+FEFF found for key testId at index 0 while processing CSV.
Unwanted U+FEFF found for key assertionId at index 0 while processing CSV.

Found this to be coming from tests/menu-button-actions-active-descendant/data/tests.csv and tests/menu-button-actions-active-descendant/data/assertions.csv. This PR updates the message to add more detail and to remove the invisible character from both files:

[tests/menu-button-actions-active-descendant]: Unwanted U+FEFF found for key testId at index 0 while processing tests.csv.
[tests/menu-button-actions-active-descendant]: Unwanted U+FEFF found for key assertionId at index 0 while processing assertions.csv.

Seems this was introduced in #1092.

[IsaDC]

Thank you @howard-e
That error confused me a few times.

[nschonni]

May want to update https://github.com/w3c/aria-at/blob/master/.gitattributes to opt everything into eol=lf

[howard-e]

@IsaDC said:

Thank you @howard-e That error confused me a few times.

No problem! I also confirmed that this won't create a new version in the app because the test content hasn't actually changed so if all is well to you here, feel free to merge!

[howard-e]

May want to update https://github.com/w3c/aria-at/blob/master/.gitattributes to opt everything into eol=lf

@nschonni certainly could expand to include *.csv. Although the relation between eol and u+feff in this file is lost on me here. Is there?

[nschonni]

You're right, it looks like there isn't anything native to git that will clean out the BOM. The encoding is set in .editorconfig, but I'm not sure how that would be enforced

[stalgiag]

Thanks for this! I needed to use the changes in this PR to make sense of the error I was seeing in the console in #1105 . I can confirm that these changes are helpful and necessary!