Add pdsg (palladium spirv-generator)

- remove glslang from pd-system
- use spirv blobs instead of glsl 460
- Use Legacy shaders for OpenGL2 backend
- add devnotes

backends/README.md

@@ -0,0 +1,24 @@
+# Backends
+
+- [Graphics](#graphics)
+  - [OpenGL2](#opengl2-legacy)
+  - [OpenGL3](#opengl3-modern-opengl)
+  - [DirectX9](#directx9-could-potentially-cover-more-then-opengl2)
+  - [Citro3D](#citro3d-3ds)
+
+## Graphics
+
+### OpenGL2 (Legacy)
+
+> [!NOTE]
+> As SPIRV to GLSL 120 translation doesn't work, your'e forced to write separate shaders for this backend
+
+### OpenGL3+ (Modern OpenGL)
+
+### DirectX9 (Could potentially cover more than OpenGL2)
+
+### Citro3D (3DS)
+
+> [!NOTE]
+> This backend requires shaders as binary file, directly in the code or as string for libpicasso
+> The Fragment Stage is special and is still wip