Coverage layer in wrong location when certain CRS used

[AlisterH]

Using an extent layer in WGS 84 the coverage layer polygons are far too large. I have not investigated what is going on, but perhaps our code simply does not work in a geographic coordinate system.

• maybe there is something we can check to warn the user (or cancel the operation)
• maybe we can automatically convert the extent layer to a suitable projected CRS if necessary.
  We should probably also look at always generating the coverage layer in the CRS of the print layout rather than the CRS of the input layer (also see Feature request: generate rotated grids if layout map is rotated #6).