[symfony] Add NoNullableServiceInConstructorRule

[TomasVotruba]

Adds NoNullableServiceInConstructorRule.

A constructor service dependency must not be nullable. A service is always provided by the container, so ?SomeService $service or SomeService|null $service only hides that the dependency is really required - and forces every use site into a null check that can never hit.

Left alone, as generic exceptions:

• abstract classes - a base may leave a dependency optional for a child to fill,
• values that are not services: nullable scalars and arrays, exceptions (?Throwable $previous is nullable by PHP convention) and date value objects (DateTimeInterface),
• a nullable param whose type a non-nullable sibling param already provides (a genuine optional extra),
• anonymous classes.

Covered by RuleTestCase with a report fixture (?Service + Service|null) and skip fixtures for each exception above.

Green locally: ECS, PHPStan, Rector, composer-dependency-analyser, tests.