Create a new affinity called FLEXNUM that works like NUMERIC except that it

never tries to convert integer to real or real to integer.  The affinity is
only used internally - it is not possible to create a table column with this
affinity.  This affinity is used on subqueries and views that are built off
of a compound SELECT and where the datatype is controlled by a CAST expression.
dbsqlfuzz c9ee6f9a0a8b8fefb02cf69de2a8b67ca39525c8

FossilOrigin-Name: 44135d6ea84f7ba6b36549954b38a8bc048d5ffea5a9779e35950afa4eb2dfb2

src/sqliteInt.h

@@ -2239,6 +2239,7 @@ struct CollSeq {
 #define SQLITE_AFF_NUMERIC  0x43  /* 'C' */
 #define SQLITE_AFF_INTEGER  0x44  /* 'D' */
 #define SQLITE_AFF_REAL     0x45  /* 'E' */
+#define SQLITE_AFF_FLEXNUM  0x46  /* 'F' */
 
 #define sqlite3IsNumericAffinity(X)  ((X)>=SQLITE_AFF_NUMERIC)