* Add support for screen-space contact shadows
This CL adds support and always enables it.
toggles and setting in the next CL (same PR).
* Plumb settings for screen-space contact shadows
screen-space contact shadows is handled like a shadow option,
parameters (including on/off) are set in the LightManager, using
the existing ShadowOptions API.
Additionally there is a per-renderable toggle.
Both toggles are off by default.
* Allow contact shadows when shadowing is auto-disabled
Shadowing can be auto-disabled when for instance there are no
shadow casters in the scene. We still allow contact shadows in
that case.
This would allow for instance, to make the vegetation on a terrain
not shadow-casting, and still get some shadowing there by using
contact shadows instead.
* apply micro-shadowing after contact shadows
also, don't compute contact shadows when we know we're fully shadowed.
d54ceff7a3