FileImageDimensionsConstraintValidator does not update file size (regression)

Problem/Motivation

This a regression from #3292350: Update the file size in file_validate_image_resolution after resizing. This fix was not kept when migrating from file_validate_image_resolution()to FileValidationEvent.

When uploading an image that is larger than constraints, the image is resized, the file size reported by the file object in FileValidationEvent does not match the actual file size, all following FileValidationEvents will get the incorrect file size.

Steps to reproduce

1. Set an image field with max_resolution settings (for example user_picture in config/people/accounts/fields)
2. Add a xdebug break on core/modules/file/src/Plugin/Validation/Constraint/FileImageDimensionsConstraintValidator.php line 67
3. Upload a file bigger than the max resolution
4. When the break point is triggered, check that $file->getSize() (original size) and $image->getFileSize() (resized size) are equal
5. Step to line 69 (after the save), compare again the values: $file->getSize() (original size) is bigger than $image->getFileSize() (resized size)
6. After image is saved, check that the size is correct in the file_managed table

Another test is to install and enable the ClamAV contrib module, the image upload will timeout with an error message from ClamAV (because send filesize and actual file size are different)

Proposed resolution

Port the previous fix to FileImageDimensionsConstraintValidator.

Remaining tasks

Test out the merge request

User interface changes

None

Introduced terminology

None

API changes

None