Modernize foreach docs (#4451)

* Use branches and statement_list for pseudocode

* Mention `Traversable` and clarify into wording

* Mention array destructuring in `list()` examples

Implicitly preferring the use of [] by mentioning it first in the examples as this seems to be the more widely used syntax these days

* Deprioritize foreach with references and use short array syntax in examples

* Reword to avoid personalization

Author: edorian