Updating Twenty Nineteen, the new default theme for 2019.

This update changes the following:

- Properly sets the primary color hue theme option. See https://github.com/WordPress/twentynineteen/pull/683.
- Add proper frontend styles for center aligned archive and category blocks. See https://github.com/WordPress/twentynineteen/pull/684.
- Fix `image_filter` theme option conditional function. See https://github.com/WordPress/twentynineteen/pull/680.
- Remove duplicate rule-line when a separator block is followed by H1/H2 in the editor. See https://github.com/WordPress/twentynineteen/pull/686.

Props richtabor, kjellr, allancole.

Merges [44192] and [44193] to trunk.

See #45424.
Built from https://develop.svn.wordpress.org/trunk@44302


git-svn-id: https://core.svn.wordpress.org/trunk@44132 1a063a9b-81f0-0310-95a4-ce76da25c4cd