feat: add MySQL support

Adds `KyselyTypegenMySQLDialect`, exported from `kysely-typegen/mysql`.

tsdown.config.ts

@@ -1,7 +1,7 @@
 import { defineConfig } from "tsdown"
 
 export default defineConfig({
-  entry: ["./src/index.ts", "./src/postgres.ts"],
+  entry: ["./src/index.ts", "./src/mysql.ts", "./src/postgres.ts"],
   dts: true,
   exports: true,
 })