[8.x] Add GIF, WEBP, WBMP, BMP support to FileFactory::image()

[AmirRezaM75]

#37742
Currently, when generating dummy images for testing, FileFactory::image() always creates a PNG or JPEG file.
PNG is default for other extensions (like gif):

return new File($name, $this->generateImage(
      $width, $height, Str::endsWith(Str::lower($name), ['.jpg', '.jpeg']) ? 'jpeg' : 'png'
));

This PR checks the file extension and creates proper image.
XBM is not supported since imagexbm() needs location as second parameter.

[AmirRezaM75]

@GrahamCampbell Sry for newbi question
Is StyleCI/CLI going to fix these coding styles automatically or should I push changes manually?

[GrahamCampbell]

The fixes will be auto-applied when the PR is merged.