Rename public API methods containing 'NewLine' to 'Newline'

[icod]

Check List:

• Fixes #2754
• Unit tests : NO (see below)
• Javadoc with a code example (on API only) : NO (Updated existing JavaDoc on lowercase methods, no duplicate JavaDoc on deprecated uppercase methods)
• PR meets the contributing guidelines, I think. This is my first PR for this project. If not, let me know 🙂

Changes:

• Strings:
  • Renamed assertContainsIgnoringNewLines (uppercase) to assertContainsIgnoringNewlines (lowercase). I thought that since this classes is in the internal package, I could safely rename the method, instead of keeping the uppercase one around for backward compatibility.
• AbstractCharSequenceAssert:
  • Added containsIgnoringNewlines (lowercase)
  • Deprecated containsIgnoringNewLines (uppercase), keeping this one around for backward compatibility
  • Added isEqualIgnoringNewlines (lowercase)
  • Deprecated isEqualIgnoringNewLines (uppercase), keeping this one around for backward compatibility
• Unit tests: Updated for the exisiting public methods, didn't add any new unit tests for the deprecated methods. If required, I can add them.

Please note

• SonarLint throws up warnings about blocking issues: the uppercase and lowercase method names are confusing.
• I have not copied the JavaDoc from the lowercase methods to the uppercase methods.

Not changed:

• Errors concerning the aforementioned assertions:
  • Class ShouldBeEqualIgnoringNewLines and its factory method shouldBeEqualIgnoringNewLines;
  • Class ShouldBeEqualIgnoringNewLineDifferences and its factory method shouldBeEqualIgnoringNewLineDifferences.

These can be changed, but I'm not sure how to name them. Change only the factory methods? Add a lowercase factory method? Duplicate the entire class (to lowercase) and deprecate the uppercase one?