Replaces all image tags in the given fileContent with corresponding img tags.
The fileContent is expected to be a string containing HTML-like content.
The image tags are expected to have the format <image ... />.
The replacement is done by matching the id attribute of each image tag with the id of an FB2Image object in the images list.
If a matching FB2Image object is found, the image tag is replaced with an img tag containing the base64-encoded image bytes.
If no matching FB2Image object is found, the image tag is left unchanged.
Returns the modified fileContent string.