Issue #2669978 by Jo Fitzgerald, arturs.v, phenaproxima: Migrate D7 Menu Links

...s/menu_link_content/migration_templates/d6_menu_links.yml

...s/menu_link_content/migration_templates/d7_menu_links.yml

...ink_content/src/Plugin/migrate/process/d7/InternalUri.php

...ntent/tests/src/Kernel/Migrate/d6/MigrateMenuLinkTest.php

...ntent/tests/src/Kernel/Migrate/d7/MigrateMenuLinkTest.php

...ts/src/Unit/Plugin/migrate/process/d7/InternalUriTest.php

core/modules/migrate_drupal/tests/fixtures/drupal7.php

...modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php

...es/migrate_drupal_ui/src/Tests/d7/MigrateUpgrade7Test.php

core/modules/shortcut/migration_templates/d7_shortcut.yml

...ut/tests/src/Kernel/Migrate/d7/MigrateShortcutSetTest.php

...sts/src/Kernel/Migrate/d7/MigrateShortcutSetUsersTest.php

...rtcut/tests/src/Kernel/Migrate/d7/MigrateShortcutTest.php

core/modules/system/migration_templates/d6_menu.yml

core/modules/system/migration_templates/d7_menu.yml

...es/system/tests/src/Kernel/Migrate/d6/MigrateMenuTest.php

...es/system/tests/src/Kernel/Migrate/d7/MigrateMenuTest.php