Implement DirectionalLight2D

[reduz]

Also separated Light2D in PointLight2D and DirectionalLight2D.

Used PointLight2D because its more of a point, and it does not work
the same as OmniLight (as shape depends on texture).

Added a few utility methods to Rect2D I needed.

[Calinou]

As for the naming, if PointLight2D turns out to be too confusing or difficult to search for, I think we could name it OmniLight2D for consistency with 3D. Sure, you can also use PointLight2D to create spotlights, but you can also do that in 3D by adding a projector texture that makes your OmniLight3D look like a SpotLight3D.

[reduz]

@Calinou The problem is that, most nodes in 2D and 3D work the same and have the same options when they have the same name. PointLight2D works quite different to OmniLight3D and SpotLight3D. At much it could be renamed to PositionalLight2D, but I think Point makes more sense.

[clayjohn]

There is something wrong with blend_mode if you change it the entire thing stops working.

More specifically, if you change the blend_mode to mix then the light disappears and it doesnt come back until you restart the engine.

[mrjustaguy]

TextureLight2D could work if it depends on the texture, however PointLight2D is I'd say ok.

Changes done.

[akien-mga]

Thanks!

[h0lley]

@reduz I am trying to reconstruct this demo compiling from this commit, but seem to be unable to.
any chance you still have the demo files & can share?

edit: nevermind, the issue was that I wasn't using normal maps.
without normal maps, blending seems to be broken. see #49922