Review the WordPressVIPMinimum.Performance.CacheValueOverride sniff

Review the `WordPressVIPMinimum.Performance.CacheValueOverride` sniff for the following in as far as relevant to that sniff:

- [ ] Code style independent sniffing / Correct handling of quirky code
Typical things to add tests for and verify correct handling of:
- [x] Nested function/closure declarations
- [x] Nested class declarations
- [ ] Comments in unexpected places
- [ ] Variables being assigned to via `list` statements
- [ ] Multiline text strings
- [ ] Text strings provided via heredoc/nowdoc
- [ ] Use of short open tags
- [ ] Using PHP close tag as end of statement
- [ ] Inline control structures (without braces)
- [ ] Code simplifications which can be made using PHPCSUtils
- [x] Sniff stability improvements which can be made using PHPCSUtils
- [ ] Correct handling of modern PHP code
Typical things to add tests for and verify correct handling of (where applicable):
- [ ] PHP 5.0 Try/catch/finally (PHP 5.5) and exceptions
- [x] PHP 5.3 Namespaced code vs code in the global namespace
- [ ] PHP 5.3 Use import statements, incl aliasing
- [ ] PHP 5.3 Short ternaries
- [x] PHP 5.3 Closures, incl closure use
- [ ] PHP 5.4 Short arrays
- [ ] PHP 5.5 Class name resolution using `::class`
- [ ] PHP 5.5 List in foreach
- [ ] PHP 5.5/7.0 Generators using yield and yield from
- [ ] PHP 5.6 Constant scalar expressions
- [x] PHP 5.6 Importing via `use function/const`
- [ ] PHP 7.0 Null coalesce
- [x] PHP 7.0 Anonymous classes
- [ ] PHP 7.0 Scalar and return type declarations
- [ ] PHP 7.0 Group use statements
- [ ] PHP 7.1 Short lists
- [ ] PHP 7.1 Keyed lists
- [ ] PHP 7.1 Multi-catch
- [ ] PHP 7.1 Nullable types
- [ ] PHP 7.3 List reference assignments
- [ ] PHP 7.4 arrow functions
- [ ] PHP 7.4 numeric literals with underscores
- [ ] PHP 7.4 null coalesce equals
- [ ] PHP 7.4 Typed properties
- [ ] Various versions: trailing comma's in function calls, group use, function declarations, closure use etc

Other:
- [ ] Review violation error vs warning
- [ ] Review violation severity
- [ ] Review violation message, consider adding a link
- [ ] Check open issues related to the sniff
- [ ] Review PHPDoc comments

Sniff basics, but changes need to be lined up for next major release:
- [ ] Inappropriate use of `public` properties (#234)
- [ ] Modular error codes (unique error code for each distinct message)

Once PHPCS/PHPCSUtils supports this:
- [ ] PHP 8.0 Constructor property promotion
- [ ] PHP 8.0 Union types
- [ ] PHP 8.0 `match` expressions
- [ ] PHP 8.0 Nullsafe operator
- [ ] PHP 8.0 Named arguments
- [ ] PHP 8.0 Single token namespaced names

Inizia con lo sniff WordPressVIPMinimum.Performance.CacheValueOverride e la relativa copertura di test esistente. Esamina gli elementi non ancora verificati relativi a compatibilità, PHPCSUtils, severità, messaggistica, PHPDoc e codici di errore, controllando le issue aperte correlate. Il lavoro è completato quando le lacune rilevanti sono state esaminate e risolte con test, oppure documentate come fuori ambito per la prossima major release.

Scritto dal modello di indicizzazione a partire dal testo della issue.