fix .dump export command

[sivukhin]

Context

There are few minor issues with current implementation of .dump command in the sqld:

1. It stop after first VIRTUAL TABLE or table with sqlite_ prefix - which is a bug

   $> CREATE VIRTUAL TABLE email USING fts5(sender, title, body);
   $> CREATE TABLE t ( value );
   $> INSERT INTO t VALUES (1), (2);
   $> .dump
   PRAGMA foreign_keys=OFF;
   BEGIN TRANSACTION;
   PRAGMA writable_schema=ON;
   INSERT INTO sqlite_schema(type,name,tbl_name,rootpage,sql) VALUES('table','email','email',0,'CREATE VIRTUAL TABLE email USING fts5(sender, title, body)');
   PRAGMA writable_schema=OFF;
   COMMIT;

2. It emit incorrect dump if sqld decides to preserve rowid:

   $> CREATE TABLE t ( x INTEGER PRIMARY KEY DESC );
   $> INSERT INTO t VALUES (1), (2), (10);
   $> .dump
   PRAGMA foreign_keys=OFF;
   BEGIN TRANSACTION;
   CREATE TABLE IF NOT EXISTS t ( x INTEGER PRIMARY KEY DESC );
   INSERT INTO t(rowid,x) VALUES(1);
   INSERT INTO t(rowid,x) VALUES(2);
   INSERT INTO t(rowid,x) VALUES(3);
   COMMIT;