Fix leaky allocation in text rendering

Author: tocsoft

src/ImageSharp.Drawing/Shapes/Rasterization/PolygonScanner.cs

@@ -98,7 +98,7 @@ public static PolygonScanner Create(
             IntersectionRule intersectionRule,
             MemoryAllocator allocator)
         {
-            var multipolygon = TessellatedMultipolygon.Create(polygon, allocator);
+            using var multipolygon = TessellatedMultipolygon.Create(polygon, allocator);
             var edges = ScanEdgeCollection.Create(multipolygon, allocator, subsampling);
             var scanner = new PolygonScanner(edges, multipolygon.TotalVertexCount * 2, minY, maxY, subsampling, intersectionRule, allocator);
             scanner.Init();

src/ImageSharp.Drawing/Shapes/Rasterization/ScanEdgeCollection.cs

@@ -40,7 +40,7 @@ public static ScanEdgeCollection Create(
             MemoryAllocator allocator,
             int subsampling)
         {
-            TessellatedMultipolygon multipolygon = TessellatedMultipolygon.Create(polygon, allocator);
+            using TessellatedMultipolygon multipolygon = TessellatedMultipolygon.Create(polygon, allocator);
             return Create(multipolygon, allocator, subsampling);
         }
     }