[Documentation] Missing docs for several methods in @ember/helper

[ef4]

The docs for the @ember/helper module are missing several exports that are public API of that module:

• array
• concat
• fn
• get
• hash

They appear instead in Ember.Templates.helpers.

As we're rolling out handlebars strict mode it becomes important to distinguish between the built-in template keywords like yield and the importable helpers like fn.