Raise the error that includes an error message

[ghiculescu]

Because of the change in #414, this line now raises an error with no helpful message on what you should do to fix it:

SessionsControllerTest#test_auth_for_invited_user:
ActionView::Template::Error: owner-banner.png
    /Users/alex/.rvm/gems/ruby-2.7.2/gems/sprockets-rails-3.2.2/lib/sprockets/rails/helper.rb:372:in `raise_unless_precompiled_asset'

Instead, we should raise the new error class added in #414

This would be a breaking change if you had code that looks like this:

    begin
      @view.javascript_include_tag("not_precompiled")
    rescue StandardError => e
      puts "error" if e.class == Sprockets::Rails::Helper::AssetNotPrecompiled
    end

But that's not very good code. A more normal rescue statement still works fine:

    begin
      @view.javascript_include_tag("not_precompiled")
    rescue Sprockets::Rails::Helper::AssetNotPrecompiled => e
      puts "error"
    end

cc @schneems