Add SolidShape2D class

[kitbdev]

SolidShape2D
Fixes #6750

Adds a new class SolidShape2D that draws a Shape2D to the screen.
Similar to Polygon2D but it draws a selected shape in a color.

[vnen]

The icon is strange because it's not solid.

[kitbdev]

updated icon to be solid

[ghost]

*/ is not aligned. 😛

[toby3d]

Does this node support drawing only the edges, without pouring?
If yes (which would be cool), then, probably, the current node name is not entirely correct.

[kitbdev]

@toby3d Nope, there is no edge only drawing support. All this class does is use the existing shape2d class to draw. I couldn't call it Shape 2D as it was taken so I went for Solid Shape 2D. If you have any suggestions for the name, let me know!

[toby3d]

@ianb96 Wait, Godot now support drawing simple figures by Shape2D?

[kitbdev]

@toby3d No, Shape2D is just used to select the shape type, like circle, square, or arrow. It is used in CollisionShape2D, and it can draw to the screen, but only to show you what the collision will be like. You cannot make your own Shape2D Node to add to your scene.

[eon-s]

Solid looks like a physics object, it can be called Geometry2D instead (and probably make use of the new meshes in 2D and textures too, but first may need to be added as it is now).

[reduz]

I Was thinking that, instead of this, a CSG system for 2D and 3D could be done..

[kitbdev]

A Constructive Solid Geometry system sounds good, I haven't heard of a 2D version of it before.
Related #17411 ?
This PR is just a simple wrapper class for prototyping purposes, so we don't have to merge it or anything.
Although, a full CSG system may take a while to implement and this could be a quick temporary solution.

[akien-mga]

We briefly discussed it with @reduz and feel that this would be better suited as a GDScript addon defining a custom node type, instead of new core Node. You can see CircleContainer for a 2.1 example of how to register such a custom node type.

Sorry for the huge delay reviewing it though, we're still catching up with the 3.0 release backlog.