Issue #2876085 by heddn, maxocub, phenaproxima, Jo Fitzgerald, vasi, quietone, yoroy, masipila, larowlan, neclimdul, krystalcode, catch: Before upgrading, audit for potential ID conflicts

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 #2787619 by hussainweb, phenaproxima, alexpott: CckMigration does not type hint CckPluginManager correctly

Issue #2598038 by alexpott, sethcardoza, quietone, Jaesin: Invalid passwords after D7 to D8 migration

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

Issue #2676222 by alexpott, johnrosswvsu: Move MigrationInterface out of the migrate\Entity namspace now they are plugins

Issue #2625696 by chx, benjy, alexpott, catch, mikeryan, andypost, phenaproxima: Make migrations themselves plugins instead of config entities

Revert "Issue #2625696 by chx, alexpott, benjy, mikeryan, andypost, phenaproxima: Make migrations themselves plugins instead of config entities"

This reverts commit 694994fe.

Issue #2625696 by chx, alexpott, benjy, mikeryan, andypost, phenaproxima: Make migrations themselves plugins instead of config entities

Issue #2590993 by mikeryan, webflo, svendecabooter, dixon_, phenaproxima: Create stub entities with proper default values

Issue #2606466 by mikeryan, Wim Leers, phenaproxima, quietone: Migration of uid 1 breaks batch upgrade process

Issue #2534042 by mikeryan, phenaproxima: Move module-specific migration support into the user module

Issue #2213451 by andypost, bdone, benjy, penyaskito, chx, claudiu.cristea, damiankloip, gregboggs, InternetDevels, jessehs, jhedstrom, marvil07, mikeryan, pcambra, Xano, YesCT: Update Migrate API in core