Sometimes we want to inflate a polygon without adding rounded edges.
This add the option using the jtMiter setting.
This is used in the Eagle parser to expand the Eagle zones for KiCad.
Eagle Zones are drawn on the polygon edge, so they extend out from the
outline. KiCad zones are drawn inside the polygon. We need to both
increase the zone size and decrease the minimum pen width to account for
this.
Fixes: lp:1817312
* https://bugs.launchpad.net/kicad/+bug/1817312
(cherry picked from commit 490c805319)
6f34f95c52