This places the arc approximation setting in the kicad_pcb file and uses
it for all parts of the board rendering where arcs are converted to
segments. This allows the user to customize their speed vs. accuracy
tradeoff. The default setting of maximum error of 0.005mm is acceptable
for small boards on moderate systems.
For legacy boards, the setting is picked up from the board outline
thickness. If the board outline has mixed thicknesses, then the
max is used and a warning is displayed.
Fixes: lp:1797787
* https://bugs.launchpad.net/kicad/+bug/1797787
jean-pierre charras
Seth Hillbrand
Jeff Young