✨ [Story Preview] Allow all story pages and grid layers to be rendered in preview mode

[coreymasanto]

• Part of I2I: Introduce PREVIEW visibility state #37129

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previewAllowed() was defaulting to prerenderAllowed() behavior for story pages and grid layers, but this behavior only allows the first story page and its grid layers to be rendered. In preview mode, all pages and grid layers must be rendered so that they can be seen in the SERP while the story auto-advances.

[amp-owners-bot]

Hey @gmajoulet, @newmuis! These files were changed:

extensions/amp-story/1.0/amp-story-grid-layer.js
extensions/amp-story/1.0/amp-story-page.js
extensions/amp-story/1.0/test/test-amp-story-page.js

[gmajoulet]

Can you host demos for these PRs so I can help you with manual testing as well? Code LGTM : ))

[ampprojectbot]

Warning: disparity between this PR Percy build and its main build

The Percy build for this PR was approved (either manually by a member of the AMP team, or automatically if there were no visual diffs). However, during a continuous integration step we generated another Percy build using the commit on the main branch that this PR was merged into, and there appears to be a mismatch between the two.

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