Switch the wide pipeline over to using floating point

Switch the wide pipeline over to using floating point

In pixman-bits-image.c, remove bits_image_fetch_untransformed_64() and
add bits_image_fetch_untransformed_float(); change
dest_get_scanline_wide() to produce a floating point buffer,

In the gradients, change *_get_scanline_wide() to call
pixman_expand_to_float() instead of pixman_expand().

In pixman-general.c change the wide Bpp to 16 instead of 8, and
initialize the buffers to 0 to prevent NaNs from causing trouble.

In pixman-noop.c make the wide solid iterator generate floating point
pixels.

In pixman-solid-fill.c, cache a floating point pixel, and make the
wide iterator generate floating point pixels.

Bug fix in bits_image_fetch_untransformed_repeat_normal