shader: Move Node declarations out of the shader IR header

Analysis passes do not have a good reason to depend on shader_ir.h to
work on top of nodes. This splits node-related declarations to their own
file and leaves the IR in shader_ir.h

src/video_core/CMakeLists.txt

@@ -104,6 +104,7 @@ add_library(video_core STATIC
     shader/decode.cpp
     shader/node_helper.cpp
     shader/node_helper.h
+    shader/node.h
     shader/shader_ir.cpp
     shader/shader_ir.h
     shader/track.cpp