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/source/gfx_opengl3.cpp

@@ -11,14 +11,18 @@
 
 namespace PD {
 void GfxOpenGL3::SysInit() {
-  SpirvHelper::Init();
-  auto vshader =
-      SpirvHelper::GLSL2SPV(SpirvHelper::Stage::Vertex, Shaders::VertCode);
-  auto fshader =
-      SpirvHelper::GLSL2SPV(SpirvHelper::Stage::Fragment, Shaders::FragCode);
-  SpirvHelper::Finalize();
-  std::string vcode = SpirvHelper::SPV2GLSL(vshader, 330, false);
-  std::string fcode = SpirvHelper::SPV2GLSL(fshader, 330, false);
+  std::string vcode = SpirvHelper::SPV2GLSL(
+      std::vector<unsigned int>(
+          Shaders::VertexShader,
+          Shaders::VertexShader +
+              (sizeof(Shaders::VertexShader) / sizeof(unsigned int))),
+      330, false);
+  std::string fcode = SpirvHelper::SPV2GLSL(
+      std::vector<unsigned int>(
+          Shaders::FragmentShader,
+          Shaders::FragmentShader +
+              (sizeof(Shaders::FragmentShader) / sizeof(unsigned int))),
+      330, false);
   PDLOG("Vertex: \n{}", vcode);
   PDLOG("Fragment: \n{}", fcode);
   pShader = CreateShaderProgram(vcode.c_str(), fcode.c_str());