Replace the newlines in nl2br()

Description

The function name of nl2br() suggests that it is a "replace" operation but is actually an "insert" operation.

Would it be possible to add a 3rd parameter so the function would actually replace the newline characters?

nl2br(string $string, bool $use_xhtml = true, bool $replace = false): string

The confusion with the name and the need for the 3rd parameter is obvious in the user contributed notes (most popular one and following ones): https://www.php.net/manual/en/function.nl2br.php#49516

The advantages of the 3rd parameter (instead of changing the behavior):

• nl2br() would be idempotent when 3rd parameter is set to true. Today n2br() cannot be applied several times to a string without managing extra inserts.
• Simplify the code. We could remove the wrappers to replace the newlines from our code.
• Flexibility. Old behavior could be kept.
• Backward compatible.

首先在 php-src 中找到 nl2br() 的实现及其测试，然后将当前的插入行为与提议的 replace 参数进行比较。完成的标准是：第三个参数默认保留现有行为，并在启用时替换换行字符，同时覆盖这两种模式。