Issue #1848266 by alexpott: Convert Diff into a proper, PSR-0-compatible PHP component.

core/core.services.yml

core/lib/Drupal/Component/Diff/Diff.php

core/lib/Drupal/Component/Diff/DiffFormatter.php

core/lib/Drupal/Component/Diff/Engine/DiffEngine.php

core/lib/Drupal/Component/Diff/Engine/DiffOp.php

core/lib/Drupal/Component/Diff/Engine/DiffOpAdd.php

core/lib/Drupal/Component/Diff/Engine/DiffOpChange.php

core/lib/Drupal/Component/Diff/Engine/DiffOpCopy.php

core/lib/Drupal/Component/Diff/Engine/DiffOpDelete.php

...lib/Drupal/Component/Diff/Engine/HWLDFWordAccumulator.php

core/lib/Drupal/Component/Diff/MappedDiff.php

core/lib/Drupal/Component/Diff/WordLevelDiff.php

core/lib/Drupal/Core/Config/ConfigManager.php

core/lib/Drupal/Core/Diff/DiffFormatter.php

core/modules/config/src/Controller/ConfigController.php

core/modules/config/src/Tests/ConfigDiffTest.php

core/modules/system/config/install/system.diff.yml

core/modules/system/config/schema/system.schema.yml