Recent Posts Widget: Use `ob_end_flush()` instead of `ob_flush()`.

`ob_end_flush()` flushes the output buffer *and* turns output buffering off, same as `ob_get_flush()`.

props m_i_n.
see #28009 for trunk.

Built from https://develop.svn.wordpress.org/trunk@28217


git-svn-id: http://core.svn.wordpress.org/trunk@28047 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Revert [28217].

Misfired commit for #27936.
Built from https://develop.svn.wordpress.org/trunk@28218


git-svn-id: http://core.svn.wordpress.org/trunk@28048 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Customizer: Allow to skip cropping header images if image width is smaller than or equal to theme width.

Add tests.

see #27936 for trunk.
Built from https://develop.svn.wordpress.org/trunk@28219


git-svn-id: http://core.svn.wordpress.org/trunk@28049 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Improve TinyMCE string for paste command browser support.

props ebinnion.
fixes #27988.

Built from https://develop.svn.wordpress.org/trunk@28220


git-svn-id: http://core.svn.wordpress.org/trunk@28050 1a063a9b-81f0-0310-95a4-ce76da25c4cd