support BITMAPV5HEADER in getimagesize()

https://en.wikipedia.org/wiki/BMP_file_format#DIB_header_.28bitmap_information_header.29

added test image:
ext/standard/tests/image/test1bpix.bmp

and adapted tests:
ext/standard/tests/image/getimagesize.phpt
ext/standard/tests/image/image_type_to_mime_type