Align the featured image to center, not full.

[jffng]

Fixes #3805.

Before	After

[kjellr]

I don't think this fixes it — we'd like our featured images to be full-width, but we also want them to actually extend to the edges of the screen. Right now when they're alignfull, they don't go all the way to the edges like an alignfull image would.

[jffng]

@kjellr

This PR does allow the featured image to extend to edges of the screen, so long as its intrinsic width is greater than or equal to the window size:

Are you suggesting that the featured image should always stretch to fullscreen, even if its width is smaller than the browser viewport?

[kjellr]

Are you suggesting that the featured image should always stretch to fullscreen, even if its width is smaller than the browser viewport?

Yeah, that would match the "alignfull" behavior of all other blocks.

[jffng]

Closing this, as it should be addressed upstream.