Add an experimental location(X) SQL function that attempt to return the

location of the payload within the database for the record that contains
column X.  location(X) returns NULL if X is not an ordinary table column or
if SQLite cannot figure out the location because it is using a covering index.

FossilOrigin-Name: 51be9558164301c5dd4df23ab8b3e67de0b522f8d36f79f3d84d45d3dc2a83a4

src/sqliteInt.h

@@ -1630,6 +1630,7 @@ struct FuncDestructor {
 #define SQLITE_FUNC_SLOCHNG  0x2000 /* "Slow Change". Value constant during a
                                     ** single query - might change over time */
 #define SQLITE_FUNC_AFFINITY 0x4000 /* Built-in affinity() function */
+#define SQLITE_FUNC_LOCATION 0x8000 /* Built-in location() function */
 
 /*
 ** The following three macros, FUNCTION(), LIKEFUNC() and AGGREGATE() are