Linked stylesheets don't preserve correct order

According to the code and comments, the order between linked stylesheets and the amp-custom style should be preserved, which makes sense, as you'd want to keep CSS ordering intact.

However, the expected output in the spec files does not match this order.

For this input:

https://github.com/ampproject/amp-toolbox/blob/v2.0.0-alpha.6/packages/optimizer/spec/transformers/valid/ReorderHeadTransformer/preserves_amp_custom_style_order/input.html#L7-L9

I would expect the output to have the exact same ordering of the two fonts and the `` tag.

However, the `expected_output.html` file shows a different order:

https://github.com/ampproject/amp-toolbox/blob/v2.0.0-alpha.6/packages/optimizer/spec/transformers/valid/ReorderHeadTransformer/preserves_amp_custom_style_order/expected_output.html#L7-L8

Compare the linked input.html and expected_output.html fixtures under packages/optimizer/spec/transformers/valid/ReorderHeadTransformer/preserves_amp_custom_style_order/. Check the ReorderHeadTransformer spec to confirm the intended stylesheet and amp-custom ordering, then run that spec and ensure the expected output matches the preserved order.

Written by the indexing model from the issue text.