take ownership of triangulation memory - OOM errors

[JonasIsensee]

Currently, I observe the following steady increase in memory upon repeated triangulations
eventually leading to OOM errors:

julia> using GeometryBasics

julia> points = Point2f.(reverse.(sincos.(0:0.01:2π)));

julia> triang = GeometryBasics.earcut_triangulate([points]);

julia> Sys.maxrss()/2^20
433.01171875

julia> @time for i=1:10^5
         GeometryBasics.earcut_triangulate([points]);
       end
 19.742204 seconds (500.00 k allocations: 30.518 MiB, 0.06% gc time)

julia> GC.gc(true)

julia> Sys.maxrss()/2^20
1156.88671875

julia> @time for i=1:10^5
         GeometryBasics.earcut_triangulate([points]);
       end
 19.175300 seconds (500.00 k allocations: 30.518 MiB)

julia> GC.gc(true)

julia> Sys.maxrss()/2^20
1873.0859375

With this PR:

julia> points = Point2f.(reverse.(sincos.(0:0.01:2π)));

julia> triang = GeometryBasics.earcut_triangulate([points]);

julia> Sys.maxrss()/2^20
411.16796875

julia> @time for i=1:10^5
         GeometryBasics.earcut_triangulate([points]);
       end
 21.869706 seconds (500.00 k allocations: 748.062 MiB, 1.02% gc time)

julia> GC.gc(true)

julia> Sys.maxrss()/2^20
438.33203125

julia> @time for i=1:10^5
         GeometryBasics.earcut_triangulate([points]);
       end
 21.142299 seconds (500.00 k allocations: 748.062 MiB, 0.17% gc time)

julia> GC.gc(true)

julia> Sys.maxrss()/2^20
438.33203125