Some users may prefer viewing images with an alpha channel without a
background. Before D11629 this was the behaviour for SVGs, but is now
impossible for both SVGs and raster images. This patch adds this option,
effectively adding functionality for raster images, and getting back the
previous behaviour for SVGs.
For raster images, choosing {nav None} paints the buffer with
`Qt::transparent` where needed.
For SVGs, this option doesn't draw anything, which was the beheviour before
D11629.
After adding this, the fade animation between two images caused ugliness
when fading from e.g. a wallpaper to a raster image with transparency.
The changes to `documentviewcontainer` and `documentview` fix the fade
animation so all fades are smooth and seemless. This also happened to
fix the small issue where the fade from raster to SVG (with `None`
background) caused the SVG to appear instantly rather than fade in.
Depends on D11629
Config option:
{F5764316}
Example (PNG on left, SVG on right):
{F5764317}
Fullscreen:
{F5766995}
New fade animation between SVG, raster (transparency), raster (no transparency):
{F5766994}