Fix #139565: PyGPU: Add builtin point shaders

This PR adds builtin shaders for drawing points. Using `FLAT_COLOR`,
`SMOOTH_COLOR`, `UNIFORM_COLOR` can lead to undesired behavior
on Metal and Vulkan backends. To ensure future compatibility this PR
adds `POINT_FLAT_COLOR` and `POINT_UNIFORM_COLOR`.

The point size can be set using `gpu.state.point_size_set`.

Pull Request: https://projects.blender.org/blender/blender/pulls/139583

source/blender/gpu/GPU_shader_builtin.hh

@@ -104,6 +104,8 @@ enum eGPUBuiltinShader {
    */
   GPU_SHADER_3D_FLAT_COLOR,
   GPU_SHADER_3D_POLYLINE_FLAT_COLOR,
+  GPU_SHADER_3D_POINT_FLAT_COLOR,
+
   /**
    * Take a 3D position and color for each vertex with perspective correct interpolation.
    *
@@ -112,6 +114,7 @@ enum eGPUBuiltinShader {
    */
   GPU_SHADER_3D_SMOOTH_COLOR,
   GPU_SHADER_3D_POLYLINE_SMOOTH_COLOR,
+
   /**
    * Take a single color for all the vertices and a 3D position for each vertex.
    *
@@ -120,6 +123,8 @@ enum eGPUBuiltinShader {
    */
   GPU_SHADER_3D_UNIFORM_COLOR,
   GPU_SHADER_3D_POLYLINE_UNIFORM_COLOR,
+  GPU_SHADER_3D_POINT_UNIFORM_COLOR,
+
   /**
    * Draw a texture in 3D. Take a 3D position and a 2D texture coordinate for each vertex.
    *