SchemaValidator: Adapting to new DBAL mapping of bigint

[ThomasLandauer]

Closes #11377

[greg0ire]

Have you tried that on a real project?

[ThomasLandauer]

• With the current BigIntType::class => 'string', I'm getting the mapping error with:

  private ?int $foo = null;

  But not with:

  private string|array|null $foo = null; // i.e. `string` doesn't have to be the only type

• With the new BigIntType::class => 'string|int', I'm still getting it with:

  private ?int $foo = null;

  But not with any of these:

  private string|int|null $foo = null;
  private int|string|null $foo = null; // i.e. order doesn't matter
  private string|int|array|null $foo = null; // i.e. some "bogus" alternative like `array` is still allowed

  => So this does indeed look like a step forward to me.

[ThomasLandauer]

In https://github.com/doctrine/orm/pull/11399 I started over (using git CLI ;-) so I'm closing here.