Function check_capitalisation 

pub fn check_capitalisation(
    rule_code: &'static str,
    category: &str,
    text: &str,
    expected: &str,
    policy_name: &str,
    span: Span,
) -> Option<LintViolation>

Check capitalisation of a token and return a violation if it doesn’t match. Shared by CP01, CP04, CP05 to avoid duplicating violation creation.