Blender Git Loki

Spreadsheet: support showing data from original/unevaluated object

There are two caveats of the current implementation which still need
to be resolved in a separate step:
* In theory the data on the original object can be editable in the spreadsheet.
* If a complex object is in edit mode, and its original data is displayed,
the drawing code can be slow, because the bmesh is converted to a mesh
every time. The proper solution is to draw the data from the bmesh directly.
This should become easier after an upcoming refactor.

Ref T86141.

Differential Revision: https://developer.blender.org/D10701