Show the paragraph and field label of fields that fail validation

A little bit adjusted patch from #16.
Now it also tries to display the actual field name from nested paragraph.

Marked NR to initiate testing on #17.

The last submitted patch, 15: 3027525-14.patch, failed testing. View results →
- codesniffer_fixes.patch Interdiff of automated coding standards fixes only.

The last submitted patch, 17: 3027525_17.patch, failed testing. View results →
- codesniffer_fixes.patch Interdiff of automated coding standards fixes only.

#17 works fine here when a required field inside a collapsed paragraph have a null value

• Encountered an error when validation fails on a field without a label property. Fixed by using the getLabel() method.
• Update test to check for the improved error message contents.

Tested on Drupal 10.3.0-dev and Paragraphs 8.x-1.17

Paragraph label is displayed in the error message. Collapsing a required paragraph also triggers validation. We can confirm that the error message is triggered at both the node level and paragraph level.

RTBC