Internals: Rename Ast on non-node classes (#3262). No functional change.

This commit has the following replacements applied:

	s/\bAstUserInUseBase\b/VNUserInUseBase/g;
        s/\bAstAttrType\b/VAttrType/g;
        s/\bAstBasicDTypeKwd\b/VBasicDTypeKwd/g;
        s/\bAstDisplayType\b/VDisplayType/g;
        s/\bAstNDeleter\b/VNDeleter/g;
        s/\bAstNRelinker\b/VNRelinker/g;
        s/\bAstNVisitor\b/VNVisitor/g;
        s/\bAstPragmaType\b/VPragmaType/g;
        s/\bAstType\b/VNType/g;
        s/\bAstUser1InUse\b/VNUser1InUse/g;
        s/\bAstUser2InUse\b/VNUser2InUse/g;
        s/\bAstUser3InUse\b/VNUser3InUse/g;
        s/\bAstUser4InUse\b/VNUser4InUse/g;
        s/\bAstUser5InUse\b/VNUser5InUse/g;
        s/\bAstVarType\b/VVarType/g;

src/V3EmitV.cpp

@@ -824,7 +824,7 @@ public:
                          AstSenTree* domainp, bool user3mark)
         : EmitVBaseVisitor{false, domainp}
         , m_formatter{os, prefix, flWidth} {
-        if (user3mark) AstUser3InUse::check();
+        if (user3mark) VNUser3InUse::check();
         iterate(nodep);
     }
     virtual ~EmitVPrefixedVisitor() override = default;