vlib: move the mysql/sqlite/pg/mssql modules under vlib/db (#16820)

examples/database/mysql.v

@@ -1,4 +1,4 @@
-import mysql
+import db.mysql
 
 fn main() {
 	mut conn := mysql.Connection{

examples/database/orm.v

@@ -1,6 +1,6 @@
-import sqlite
-import mysql
-import pg
+import db.sqlite
+import db.mysql
+import db.pg
 
 [table: 'modules']
 struct Module {

examples/database/psql/customer.v

@@ -1,6 +1,6 @@
 module main
 
-import pg
+import db.pg
 
 const dash = '----------------------------------------------------------------'
 

examples/database/sqlite.v

@@ -1,4 +1,4 @@
-import sqlite
+import db.sqlite
 
 fn main() {
 	db := sqlite.connect(':memory:')!

examples/js_dom_draw_bechmark_chart/v_vweb_orm/src/main.v

@@ -2,7 +2,7 @@ module main
 
 import vweb
 import time
-import sqlite
+import db.sqlite
 
 struct App {
 	vweb.Context

examples/vweb_orm_jwt/src/databases/config_databases_sqlite.v

@@ -1,6 +1,6 @@
 module databases
 
-import sqlite
+import db.sqlite
 
 pub fn create_db_connection() !sqlite.DB {
 	mut db := sqlite.connect('database.db')!