New Valkyrie::ID#== is not symmetric over String

[no-reply]

After Valkyrie.config.id_string_equality = true:

Valkyrie::ID.new('an_id') == 'an_id' # => true
'an_id' == Valkyrie::ID.new('an_id') #=> false

Complicating things further, these objects are symmetrically equal for purposes of #<=>:

Valkyrie::ID.new('an_id') <=> 'an_id' #=> 0
'an_id' <=> Valkyrie::ID.new('an_id') #=> 0

This can be fixed by providing a Valkyrie::ID#to_str, which will cause String to use Valkyrie::ID#== to determine == style equality.

[no-reply]

The implementation of #== in 83bf5d5 may be problematic for other reasons:

class Moomin
  def to_s
    'moomin'
  end
end

Moomin.new == Valkyrie::ID.new('moomin') # => false
Valkyrie::ID.new('moomin') == Moomin.new # => true