This was causing flashing colors in the node editor grid.
This is because in some cases the flat color is only set on the provoking
vertex which is the last of the primitive by default.
This new shader is able to emulate smooth wide lines drawing using a
geometry shader.
This shader needs viewportSize and lineWidth uniforms to be set.
There is multiple variants to replace the usage of wide lines for most
shaders.
This patch only fix the gizmo_types files and the navigation gizmo.
Other areas could be fixed afterward, I just limited the patch size.
Fix T57570.
Reviewed By: billreynish
Differential Revision: https://developer.blender.org/D7487
