svg: replace deprecated rsvg_handle_get_dimensions
Use rsvg_handle_get_intrinsic_size_in_pixels for librsvg >= 2.52 to support fractional dimensions and fix the deprecation warning.
Note that the result is currently cast to an integer to match the existing logic. If you would prefer a full refactor of DecodeBlock() to leverage the floating-point precision, I can update the patch.
Signed-off-by: Abderhman Gamal <abderhmangamal246@gmail.com>