[GIT-PULLS] [php-src] PR #22633: feat: add pipe assignment operator (`|>=`)

Pull Request: https://github.com/php/php-src/pull/22633
Author: calebdw

Hello!

This adds the `|>=` compound assignment operator for the pipe operator, allowing `$x |>= callable` to be used as shorthand for `$x = $x |> callable`.

Supports pipe chains on the RHS:
```php
$x |>= fn1(...) |> fn2(...) |> fn3(...);
// is equivalent to
$x = $x |> fn1(...) |> fn2(...) |> fn3(...);
```

Implementation modeled after `??=` (ZEND_AST_ASSIGN_COALESCE), with a dedicated AST node (ZEND_AST_ASSIGN_PIPE) and compiler function that uses memoization to avoid double-evaluating complex LHS expressions.

Extracts shared callable dispatch logic into zend_pipe_build_fcall() helper used by both `|>` and `|>=` compilation.

All variable target types supported: simple vars, array dims, object properties, static properties.

Thanks!