Revert "Issue #2033211 by LewisNyman, tim.plunkett, JamesLefrère | yannickoo: Move Seven CSS files into css directory."

This reverts commit 16e60c421b49632d3ca65664a94b44bd20703dc1.
Issue #2302843 by claudiu.cristea: {cache_tags} conflicts with cache bin database table names.
Issue #2303547 by mgifford: Fixed Consistency - screen-reader to screen reader.
Issue #2301955 by er.pushpinderrana, lokapujya | scor: Ensure RDFa metadata tags are hidden.
Issue #2298667 by Mile23, neclimdul: Fixed Code review for report generation.
Issue #2297681 by cilefen, Wim Leers, cs_shadow | Charles Belov: Added Make the "alt" attribute required in EditorImageDialog.
Issue #2268939 by Gábor Hojtsy, vijaycs85: Fixed Config overrides not updated when config changes.
Issue #2295737 by Gábor Hojtsy, vijaycs85, alexpott: Fixed Not all shipped configuration passes validation even with all modules enabled.
Issue #2303879 by slashrsm: Remove comment_get_display_ordinal().
Issue #2303883 by slashrsm: Remove comment_get_display_page().
Issue #2303887 by slashrsm: Remove comment_new_page_count().
Issue #2303719 by olli: Remove obsolete ApcuBackend::isEmpty() method.
Issue #2301273 by pwolanin, dawehner, Wim Leers, effulgentsia, joelpittet, larowlan, YesCT, kgoel: MenuLinkNG part2 (no UI or conversions): MenuLinkTree API and unit tests.
Issue #2268761 by tim.plunkett: Remove support for function-based forms.
Issue #2072897 by jayeshanandani, marcingy, herom, er.pushpinderrana, inket: Modernize contact.module forms.
Issue #2303605 by cilefen: Rename *.menu_links.yml to *.links.menu.yml files to improve DX.
Issue #2298319 by Berdir | ivanjaros: Fixed views.display.block.allow should be a sequence not a boolean.
Issue #2226063 by Berdir, plopesc: Merge ListBooleanItem from options module into BooleanItem.
Issue #2073759 by mondrake, fietserwin, claudiu.cristea: Convert toolkit operations to plugins.
Issue #2285189 by Jose Reyero, Gábor Hojtsy: Fixed Undefined config schema type should not be explicitly used in config schemas.