Fix emitting this (#5849)

src/V3EmitV.cpp

@@ -634,6 +634,7 @@ class EmitVBaseVisitorConst VL_NOT_FINAL : public EmitCBaseVisitorConst {
         iterateAndNextConstNull(nodep->fromp());
         puts(cvtToStr(nodep->declRange()));
     }
+    void visit(AstThisRef* nodep) override { puts("this"); }
     void visit(AstTypedef* nodep) override {
         putfs(nodep, "typedef ");
         iterateConstNull(nodep->subDTypep());

test_regress/t/t_debug_emitv.out

@@ -331,6 +331,9 @@ package Vt_debug_emitv___024unit;
         int signed member;
         member = 'sh1;
         task method;
+            if ((this != this)) begin
+                $stop;
+            end
         endtask
         function new;
         endfunction

test_regress/t/t_debug_emitv.v

@@ -22,6 +22,7 @@ endpackage
 class Cls;
    int member = 1;
    function void method;
+      if (this != this) $stop;
    endfunction
 endclass