Better definition for Data.String.NonEmpty.CodeUnits.fromFoldable1

[postsolar]

Current definition of Data.String.CodeUnits.NonEmpty.fromFoldable1 uses unsafeCoerce to coerce an array of characters into array of non-empty strings. This is 1) unsuitable for some backends; 2) could be redefined via singleton :: Char -> String.

I also slipped in a small doc comment update.

Checklist:

• Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation
• Added a test for the contribution (if applicable)

[natefaubion]

While this is a small internal change, I think we should still add a changelog entry.