hide images/videos in og cards, when under a CW - fixes #487

What does this PR do?

When a note has a CW, its images and videos are normally hidden in the frontend. Before this fix, the og:image and og:video:* <meta> properties (that are used by embedders to show previews) still included all images and videos that were not also marked sensitive.

This fix makes the previews behave like the normal web frontend.

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requested review from @fEmber, @Leah, and @luna

approved this merge request

approved this merge request

merged

mentioned in commit e0afeff2