Fix PHPStan missingType.generics for FieldItemListInterface not specifying its type

Problem/Motivation

Fix

i$ignoreErrors[] = [
	'message' => '#^Method Drupal\\\\Core\\\\Entity\\\\ContentEntityBase\\:\\:getTranslatedField\\(\\) return type with generic interface Drupal\\\\Core\\\\Field\\\\FieldItemListInterface does not specify its types\\: T$#',
	'identifier' => 'missingType.generics',
	'count' => 1,
	'path' => __DIR__ . '/lib/Drupal/Core/Entity/ContentEntityBase.php',
];

and similar.

Steps to reproduce

grep "FieldItemListInterface does not specify its types" -B1 -A4 core/.phpstan-baseline.php

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet