Rule request: Avoid using the Assignment by Addition Operator (`+=`) to build a string

Summary of the new feature

Strings are immutable. Each addition to the string actually creates a new string big enough to hold the contents of both the left and right operands, then copies the elements of both operands into the new string. For small strings, this overhead may not matter. For large strings, this can affect performance and memory consumption.
This will create more awareness of the possible performance impact of using the Assignment by Addition Operator (+= ), see also:

• Avoid the increase assignment operator (+=) for building strings
• PowerShell scripting performance considerations / String addition

Proposed technical implementation details (optional)

See (PowerShell based) prototype AvoidPlusEqualsToBuildStrings at: https://github.com/iRon7/PSRules

What is the latest version of PSScriptAnalyzer at the point of writing

1.21.0

Inizia esaminando il prototipo collegato AvoidPlusEqualsToBuildStrings e i riferimenti dell'issue sull'addizione di stringhe PowerShell. Poi analizza i pattern e i test delle regole esistenti di PSScriptAnalyzer. Il lavoro è completo quando una regola identifica l'uso di += per costruire stringhe e lo segnala in modo coerente con le convenzioni dell'analizzatore del progetto.