Document both the refutable and irrefutable syntax for each pattern type

[MaryaBelanger]

"... the documentation of the different kinds of patterns uses the refutable syntax for some of them, and the irrefutable syntax for others. I wonder whether it would be better to just bite the bullet and document both syntaxes for each pattern type? It would also help drive home the fact that there are two syntaxes. Example here: https://dart.dev/language/pattern-types#rest-element"

"...the docs silently go back and forth between using the irrefutable syntax (no var) and the refutable syntax."