* Split up the thirdparty code into the thirdparty folder (#3637)
* Create a new kimath static library containing all the math functions
This is part of cleaning the build system for #1906.
For items defined by 2 point, the ending point coordinates are rounded to the near integer,
but the starting point coordinates were just truncated instead of being rounding,
creating sometimes an error for horizontal or vertical lines.
Fixes: lp:1835211
https://bugs.launchpad.net/kicad/+bug/1835211
* rename WS_DRAW_ITEM_POLYGON to WS_DRAW_ITEM_POLYPOLYGONS (better name)
* use SHAPE_POLY_SET instead of std::vector(<wxPoint> to manage the set of polygons.
It also remove duplicate code related to HitTest and bounding box.
* fix HitTest and WS_DRAW_ITEM_POLYGON highlight.
Jeff Young
Ian McInerney
jean-pierre charras