Emit model implementation as loose methods. (#3006)

This patch introduces the concept of 'loose' methods, which semantically
are methods, but are declared as global functions, and are passed an
explicit 'self' pointer. This enables these methods to be declared
outside the class, only when they are needed, therefore removing the
header dependency. The bulk of the emitted model implementation now uses
loose methods.

src/V3Order.cpp

@@ -1754,14 +1754,13 @@ AstActive* OrderVisitor::processMoveOneLogic(const OrderLogicVertex* lvertexp,
             if (!newFuncpr && domainp != m_deleteDomainp) {
                 const string name = cfuncName(modp, domainp, scopep, nodep);
                 newFuncpr = new AstCFunc(nodep->fileline(), name, scopep);
-                newFuncpr->argTypes(EmitCBaseVisitor::symClassVar());
-                newFuncpr->symProlog(true);
+                newFuncpr->isStatic(false);
+                newFuncpr->isLoose(true);
                 newStmtsr = 0;
                 if (domainp->hasInitial() || domainp->hasSettle()) newFuncpr->slow(true);
                 scopep->addActivep(newFuncpr);
                 // Create top call to it
                 AstCCall* const callp = new AstCCall(nodep->fileline(), newFuncpr);
-                callp->argTypes("vlSymsp");
                 // Where will we be adding the call?
                 AstActive* const newActivep = new AstActive(nodep->fileline(), name, domainp);
                 newActivep->addStmtsp(callp);