implement a stateful PathGeometry builder and expose to DrawContext

[zwcloud]

• [x] implement usable API that can stroke and fill figures correctly
• [ ] support setting color for one single segment

This is another preparation for text-rendering unit-tests.

Currently, the only way to create a PathGeometry is adding segments one by one, adding figures one by one. https://github.com/zwcloud/ImGui/blob/accca31a7605343bd76dc76d0da74ba65736548f/src/ImGui/Control/Toggle.cs#L180-L188

ImGui shoud provide stateful APIs as a convenient alternative like the HTML's canvas 2D path APIs.

[zwcloud]

reference:

• webkit canvas 2D
  • https://github.com/WebKit/webkit/blob/c1a21624b3be026d89d161de40e96b5234cd2f2f/Source/WebCore/html/canvas/CanvasRenderingContext2DBase.cpp
  • https://github.com/WebKit/webkit/blob/e45dd864a345bb28f68bb969072a13ea75a74fdb/Source/WebCore/html/canvas/CanvasPath.h
  • https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Tutorial/Drawing_shapes
• cairo
  • https://github.com/zwcloud/CairoSharp/blob/b696af4f91ccef14aedf6902cad72a4284e2640f/source/Native/cairo/src/cairo-path-stroke-polygon.c
• WPF
  • SteamGeometry, ByteStreamGeometryContext, StreamGeometryContext

TODO StreamGeometryContext should be implemented first and the PathGeometryBuilder will be built on top of it.