Formatting: Ensure `wpautop()` isn't run on content generated from blocks.

As `do_blocks()` is run before `wpautop()` in the_content filter, we can remove in a Just In Time fashion, before that filter is run.

After `wpautop()`s original priority has passed, we can re-add it in a Just Too Late fashion, to ensure it's available if `the_content` filter is run multiple times on a page load.

Merges [43879] and [43881] from the 5.0 branch to trunk.

Props pento, nerrad.
Fixes #45290.

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git-svn-id: https://core.svn.wordpress.org/trunk@44056 1a063a9b-81f0-0310-95a4-ce76da25c4cd