Optimize CReset in Dfg (#7737)

Teach DFG about CReset. This is not so much to optimize CReset itself, but to enable synthesizing logic involving CReset, which does appear with automatic variables used only in certain branches

src/V3DfgPasses.cpp

@@ -120,6 +120,8 @@ void V3DfgPasses::inlineVars(DfgGraph& dfg) {
         // Partial driver cannot be inlined
         if (srcp->is<DfgVertexSplice>()) continue;
         if (srcp->is<DfgUnitArray>()) continue;
+        // Don't inline CReset
+        if (srcp->is<DfgCReset>()) continue;
         // Okie dokie, here we go ...
         vtx.replaceWith(srcp);
     }