Add the SQLITE_CONFIG_MEMDB_MAXSIZE configuration option for configuring

the default maximum size of an in-memory database created using
sqlite3_deserialize().  This is necessary to make the interface reasonably
testable.

FossilOrigin-Name: cb72ee0478ce98c48aae059fd5de4e36caf2b8c953e08fcb799bfd119ad46b73

src/sqliteInt.h

@@ -3428,6 +3428,9 @@ struct Sqlite3Config {
   void (*xVdbeBranch)(void*,unsigned iSrcLine,u8 eThis,u8 eMx);  /* Callback */
   void *pVdbeBranchArg;                                     /* 1st argument */
 #endif
+#ifdef SQLITE_ENABLE_DESERIALIZE
+  sqlite3_int64 mxMemdbSize;        /* Default max memdb size */
+#endif
 #ifndef SQLITE_UNTESTABLE
   int (*xTestCallback)(int);        /* Invoked by sqlite3FaultSim() */
 #endif