Issue #2873696 by nvexler, wengerk, gido, Jo Fitzgerald, xjm: Add @internal to core classes, methods, properties to Form Classes

Issue #2776975 by joelpittet, dawehner, tim.plunkett, xjm, pfrenssen: March 3, 2017: Convert core to array syntax coding standards for Drupal 8.3.x RC phase

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

Issue #2301317 by pwolanin, dawehner, Wim Leers, effulgentsia, YesCT, xjm, alexpott: MenuLinkNG part4: Conversion.

Revert "Issue #2301317 by pwolanin, effulgentsia, Wim Leers, dawehner, alexpott: MenuLinkNG part4: Conversion."

This reverts commit fd2db9cd.

Issue #2301317 by pwolanin, effulgentsia, Wim Leers, dawehner, alexpott: MenuLinkNG part4: Conversion.

Issue #2301313 by pwolanin, dawehner, Wim Leers, effulgentsia, kgoel, YesCT, glide: MenuLinkNG part3 (no conversions): MenuLinkContent UI.