[ci skip] Fix documentation for @macro and reflection types

Since `@macro` doesn't exist anymore and these reflections are no
longer AssociationReflections but their own types of reflections
based on macro I updated the documentation to match the changes I
made in #16089 and #16198. An `AssociationReflection` that had a
`@macro` of `:has_many` now is a `HasManyReflection`
Merge pull request #16315 from eileencodes/fix-documentation-that-mentions-macro-instance-var

Fix documentation for `@macro` and reflection types