Implement CAL and RET shader instructions (#1618)

* Add support for CAL and RET shader instructions

* Remove unused stuff

* Fix a bug that could cause the wrong values to be passed to a function

* Avoid repopulating function id dictionary every time

* PR feedback

* Fix vertex shader A/B merge

Ryujinx.Graphics.Shader/IntermediateRepresentation/BasicBlock.cs

@@ -24,6 +24,7 @@ namespace Ryujinx.Graphics.Shader.IntermediateRepresentation
         }
 
         public bool HasBranch => _branch != null;
+        public bool Reachable => Index == 0 || Predecessors.Count != 0;
 
         public List<BasicBlock> Predecessors { get; }