Record the position of many identifiers in the parse using the new

Expr.w.iOfst field.  This is done with the idea of providing offset
results for sqlite3_error_offset() for a more kinds of errors, though that
part is not yet implemented.

FossilOrigin-Name: 32a3a53b62ab09ac2212905e7f42fe6f1b09d891e015203e5caf4cb16262f18e

src/sqliteInt.h

@@ -2824,7 +2824,10 @@ struct Expr {
                          ** TK_VARIABLE: variable number (always >= 1).
                          ** TK_SELECT_COLUMN: column of the result vector */
   i16 iAgg;              /* Which entry in pAggInfo->aCol[] or ->aFunc[] */
-  int iRightJoinTable;   /* If EP_FromJoin, the right table of the join */
+  union {
+    int iRightJoinTable;   /* If EP_FromJoin, the right table of the join */
+    int iOfst;             /* else: start of token from start of statement */
+  } w;
   AggInfo *pAggInfo;     /* Used by TK_AGG_COLUMN and TK_AGG_FUNCTION */
   union {
     Table *pTab;           /* TK_COLUMN: Table containing column. Can be NULL