shader_ir/memory: Implement u16 and u8 for STG and LDG

Using the same technique we used for u8 on LDG, implement u16.

In the case of STG, load memory and insert the value we want to set
into it with bitfieldInsert. Then set that value.

src/video_core/shader/shader_ir.h

@@ -394,7 +394,7 @@ private:
 
     std::tuple<Node, Node, GlobalMemoryBase> TrackGlobalMemory(NodeBlock& bb,
                                                                Tegra::Shader::Instruction instr,
-                                                               bool is_write);
+                                                               bool is_read, bool is_write);
 
     /// Register new amending code and obtain the reference id.
     std::size_t DeclareAmend(Node new_amend);