BUG 15158: Enable screen shots of Spreadsheet Views

Attempting to save a screen shot from a Spreadsheet View would
result in an error message after users went through the motions
of saving an image.

This change makes it possible to save the currently rendered
content of a Spreadsheet View as an image.

Limitations:
- magnification factor is ignored
- custom image size is ignored
- The spreadsheet view is not saved out when all views in a layout are saved
Status Job ID Name Coverage
  External
passed kwrobot-branch-check