Allow correct and projected interpolation equations in single-sampled line interpolat...

Allow correct and projected interpolation equations in single-sampled line interpolation test.

- Use proper interpolation equation for verification. Do not
  approximate distance to pixel center by projecting it along major
  direction. (i.e. just selecting major compontent).
- Detect projected interpolation in interpolation tests and issue
  a QualityWarning for such implementations.
- Calculate line interpolation weights in screen space, not in clip
  space.

Bug: 19410338
Change-Id: Ie27aa9cf121d1c92c86cda19a7b8c97e132fcb66