[DomCrawler] Fixed incorrect handling of image inputs

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #10204
| License       | MIT
| Doc PR        |

A possible approach to fix #10204, but I'm open to suggestions to fix this another way, as this might not be the most 'elegant' way.

Initially, my thoughts were to create a new DomCrawler\Field\FormField subclass, especially for image inputs. However, this does not solve the problem, because such a FormField would still exist under 1 name in the FormFieldRegistry.

Instead, I've changed it to have 2 separate FormFields instead (which both reference the same input node), with different names (.x and .y) so that both values can be set separately and will both be submitted.