Preserve order when generating CSV

[pcai]

Resolves #2580

Generate CSVs using kaminari pagination when available (e.g., when @objects is an ActiveRecord_Relation) instead of using the native rails find_each.

This allows us to preserve the activerecord ORDER BY clause defined when browsing records before attempting to export them; find_each overrides the ORDER BY to use the primary key id.

One potential downside to this is that it will make certain large exports much less efficient, as paginating large tables ordered by a column without the correct database indexes will run into algorithmic problems.

Issue reproduction:

• Navigate to a records index page and change the sort ordering (e.g., sort by "Name descending"):
  
• Click "export found _____"
• generate the CSV

EXPECTED:

• the generated CSV has the sort ordering from the previous step

ACTUAL:

• the generated CSV is in primary key id order

[coveralls]

coverage: 96.044% (+0.08%) from 95.965% when pulling d90183f on pcai:order-csv-exports into e158beb on railsadminteam:master.

[kcromanpl-main]

If this is okay to you, please also consider matching whole records. This will make sure of order even for other code changes.

context 'when objects are ordered' do
  # or use before block as before
  let!(players) do
    FactoryBot.create_list :player, 2 do |player, index|
      player.name = "Player #{index}"
    end
  end

  let(:objects) { Player.all.order(name: :desc) }
  let(:options) { {} }

  # modify the subject block to return the array of objects
  it 'preserves the ordering' do
    expect(subject[2].split("\n")[1]).to eq('Player 1', 'Player 2')
  end
end

[pcai]

Thanks. I incorporated some of your suggestions, but matching the whole record is a bit nontrivial because the pk ids are not predictable when randomizing test seed