…ibraryResources task.

* Enable nullability and fix any issues.
* Improve error reporting by:
	* Not bailing out when the first error is encountered, keep processing in
	  case we can be produce and find more problems to report.
	* Show a better error message by including the path of the problematic
	  file in the error message.

Due to indentation changes, this PR migth be easier to review by hiding
whitespace differences.

…sources-nullability