Blender Git Loki

Fix border rendering for eevee + stop passing render result around

Technically the original issue is that xof/yof in render result is calculated
for drawing border render. So a simpler patch could be:

```
- rr->xof = re->disprect.xmin;
+ rr->xof = re->disprect.xmin + BLI_rcti_cent_x(&re->disprect) - (re->winx / 2);
```

However everywhere in the code we are getting border directly from re->disprect
which we may as well do here too.

Besides I'm taking this as a chance to get rid of RenderResult in the internal
loop of eevee, to help prepare the code to the upcoming rendering pipeline
changes.