Issue #2386357 by drunken monkey: Fixed testbot failures
Issue #2386309 by Berdir: Fixed fatal error during Views query build() if query was aborted.
Adapted to latest Core change: Do not use "css" in "#attached" anymore.
Removed a few sloppiness errors regarding retrieving a field's data definition or description.
Issue #2242361 by drunken monkey: Fixed some remaining snake_case properties.
Issue #2383679 by jsacksick, drunken monkey: Fixed invoking hook_search_api_index_reindex().
Issue #2383091 by jsacksick: Fixed form element dependencies on "Fields" tab.
Merge branch '8.x-1.x' into 2349435-seperate-processors-by-stage
Rename "Postprocess" stage to "Postprocess query".
Refactor the ProcessorPluginBase::$stages property to ProcessorPluginManager::getProcessingStages().
Improved plugin documentation.
Added translation to processor stage labels.
Fixed a few minor CSS issues.
Some code cleanup.
Various fixes (WIP).