fix: phpdoc syntax for repeatedfield parameters

[bshaffer]

The current way we document RepeatedField parameters is ambiguous in PHPDoc. For Collection|Foo[], two possible paths are taken:

1. If Collection implements Traversable (which RepeatedField does), Collection|Foo[] is interpreted as a Collection object that iterates over Foo. The array part isn’t applied. This is what is currently happening for Protobuf.
2. If Collection|Foo[] means “Collection or array” (which is what we mean in our case) we need to disambiguate the type by using Collection|array<Foo> instead.

This PR replaces all instance of ProtoClass[]|RepeatedField with the less-ambiguous array<ProtoClass>|RepeatedField

[perezd]

LGTM!