Issue #2936253 by gabesullice: Clarify usage of AccountProxyInterface: recommend AccountInterface for most use cases

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2286971 by znerol, Berdir, almaudoh, cilefen: Remove dependency of current_user on request and authentication manager

Issue #2378329 by almaudoh: Update AccountProxyInterface::setAccount() documentation to point people to the account_switcher service

Issue #2180109 by damiankloip, dawehner, ParisLiakos, joelpittet, MartijnBraam, Xano: Change the current_user service to a proxy.