* 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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Control can indicate its active state by a subclass overriding the 'active_callback' method, by supplying a callable 'active_callback' argument into the control's constructor, or by filtering 'customize_control_active'.
props westonruter.
see #27993.
Built from https://develop.svn.wordpress.org/trunk@29051
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* Move `WidgetCustomizerPreview` to `wp.customize.WidgetCustomizerPreview`
* Move `WidgetCustomizerPreview_exports` to export_preview_data()
* Use `_wpWidgetCustomizerPreviewSettings` to transfer settings to `wp.customize.WidgetCustomizerPreview`
see #27485.
Built from https://develop.svn.wordpress.org/trunk@27653
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