Issue #2195753 by tim.plunkett: Changes to config entities that use plugins are not propagated to the plugins.

Issue #2199483 by damiankloip, alexpott: Provide a default config_prefix based on entity type ID and provider.

Issue #2119905 by damiankloip, tim.plunkett, Berdir: Provide @ConfigEntityType and @ContentEntityType to have better defaults.

Issue #2164367 by alexpott, tim.plunkett, dawehner: Rebuild router as few times as possible per request.

Issue #2042807 by tim.plunkett, pwolanin, ianthomas_uk, jhodgdon: Convert search plugins to use a ConfigEntity and a PluginBag.