* Introduces `customize-selective-refresh-widgets` theme support feature and adds to themes.
* Introduces `customize_selective_refresh` arg for `WP_Widget::$widget_options` and adds to all core widgets.
* Remove `selective_refresh` from being a component that can be removed via `customize_loaded_components` filter.
* Add `WP_Customize_Widgets::get_selective_refreshable_widgets()` and `WP_Customize_Widgets::is_widget_selective_refreshable()`.
* Fix default `selector` for `Partial` instances.
* Implement and improve Masronry sidebar refresh logic in Twenty Thirteen and Twenty Fourteen, including preservation of initial widget position after refresh.
* Re-initialize ME.js when refreshing `Twenty_Fourteen_Ephemera_Widget`.
See #27355.
Fixes#35855.
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* `default-widgets.php` now requires all of the individual classes
* Move the functions scattered about this file to `widget-functions.php`, which loads before `default-widgets.php`, which only conditionally loads anyway in `wp_maybe_load_widgets()`, which is hooked on `plugins_loaded`
See #33413, #23012.
Built from https://develop.svn.wordpress.org/trunk@33843
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