Related #39644.

Historically subclasses of `Equality` has a special equality ability,
but it has migrated to `equality?` method.

Since we have added `HomogeneousIn`, `Equality === node` could no longer
detect all equality nodes, we should check the response of `equality?`
method for the purpose.

Originally, it wasn't common understanding that the `In` node was a
subclass of the `Equality` node, so it was unclear whether
`Equality === node` really wanted to detect the `In` node as well.

As another problem, we need to check `In === node` first if intend to
detect only `Equality` node.

Example:

https://github.com/rails/rails/blob/4148590ed99f76debd2a016ed03d2e2bd65eab37/activerecord/lib/active_record/relation/where_clause.rb#L98-L103

This solves the problems described above.