Issue #1987824 by nick_schuch, vijaycs85, ParisLiakos: Convert system_php() to a new style controller.

Issue #1987850 by oenie, vijaycs85, cosmicdreams, amateescu: Convert system_theme_disable() to a new style controller.

Issue #1946454 by andypost, kim.pepper, tim.plunkett, ParisLiakos: Convert all confirm_form() in system.module and system.admin.inc to the new form interface and convert route.

Issue #1925660 by ACF, tim.plunkett, mtift, heddn, Cottser: Convert system's system_config_form() to SystemConfigFormBase.

Issue #1842718 by alippai, andypost, alexpott, nod_: Use new Transliteration functionality in core for machine names.

Issue #1793520 by disasm, klausi, tnightingale, Crell: Add access control mechanism for new router system.