Add support for no-JS styling and noscript > style[amp-noscript]

[westonruter]

Feature description

In ampproject/amphtml#20609 AMP now allows a noscript > style[amp-noscript] to style elements on pages for which the user has JavaScript disabled. Currently the AMP plugin unwraps all noscript elements (unless they have a data-amp-no-unwrap attribute) so any nested style will then automatically be added to style[amp-custom]. However, when unwrapping has been disabled (per #6528 and #6546), any such styles should be moved not to style[amp-custom] but rather to noscript > style[amp-noscript].

See also ampproject/amp-toolbox-php#349.

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Implementation brief

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