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/CMakeLists.txt

@@ -86,12 +86,5 @@ else()
         spirv-cross-msl
         spirv-cross-reflect
         spirv-cross-util
-        glslang
-        glslang-default-resource-limits
-        #OGLCompiler
-        OSDependent
-        SPIRV
-        #SPVRemapper
-        #HLSL
     )
 endif()