feat(query): add _isfilled pseudocolumn to indicate data is origin

or filled.

source/libs/parser/inc/sql.y

@@ -733,6 +733,7 @@ pseudo_column(A) ::= WSTART(B).
 pseudo_column(A) ::= WEND(B).                                                     { A = createRawExprNode(pCxt, &B, createFunctionNode(pCxt, &B, NULL)); }
 pseudo_column(A) ::= WDURATION(B).                                                { A = createRawExprNode(pCxt, &B, createFunctionNode(pCxt, &B, NULL)); }
 pseudo_column(A) ::= IROWTS(B).                                                   { A = createRawExprNode(pCxt, &B, createFunctionNode(pCxt, &B, NULL)); }
+pseudo_column(A) ::= ISFILLED(B).                                                 { A = createRawExprNode(pCxt, &B, createFunctionNode(pCxt, &B, NULL)); }
 pseudo_column(A) ::= QTAGS(B).                                                    { A = createRawExprNode(pCxt, &B, createFunctionNode(pCxt, &B, NULL)); }
 
 function_expression(A) ::= function_name(B) NK_LP expression_list(C) NK_RP(D).    { A = createRawExprNodeExt(pCxt, &B, &D, createFunctionNode(pCxt, &B, C)); }

source/libs/parser/src/parTokenizer.c

@@ -260,6 +260,7 @@ static SKeyword keywordTable[] = {
     {"WRITE",                TK_WRITE},
     {"_C0",                  TK_ROWTS},
     {"_IROWTS",              TK_IROWTS},
+    {"_ISFILLED",            TK_ISFILLED},
     {"_QDURATION",           TK_QDURATION},
     {"_QEND",                TK_QEND},
     {"_QSTART",              TK_QSTART},