style(cspell): Fix cspell spelling and enable cspell testing (#3418190)

.cspell.json

.gitattributes

.github/workflows/testing.yml

README.md

...al/Docs/Functions/FunctionCallArgumentSpacingStandard.xml

...r/Drupal/Docs/Functions/FunctionCallSignatureStandard.xml

...iffer/Drupal/Docs/Functions/ValidDefaultValueStandard.xml

...fer/Drupal/Sniffs/CSS/ClassDefinitionNameSpacingSniff.php

coder_sniffer/Drupal/Sniffs/CSS/ColourDefinitionSniff.php

...r_sniffer/Drupal/Sniffs/Classes/ClassDeclarationSniff.php

...niffer/Drupal/Sniffs/Classes/PropertyDeclarationSniff.php

coder_sniffer/Drupal/Sniffs/Commenting/ClassCommentSniff.php

coder_sniffer/Drupal/Sniffs/Commenting/DeprecatedSniff.php

coder_sniffer/Drupal/Sniffs/Commenting/DocCommentSniff.php

coder_sniffer/Drupal/Sniffs/Commenting/FileCommentSniff.php

...sniffer/Drupal/Sniffs/Commenting/FunctionCommentSniff.php

coder_sniffer/Drupal/Sniffs/Commenting/HookCommentSniff.php

...r_sniffer/Drupal/Sniffs/Commenting/InlineCommentSniff.php

...sniffer/Drupal/Sniffs/Commenting/VariableCommentSniff.php

.../Sniffs/ControlStructures/InlineControlStructureSniff.php