add endtoend tests for mysql and postgres stdlib

internal/endtoend/testdata/sqlc_embed/mysql/query.sql

@@ -0,0 +1,29 @@
+CREATE TABLE users (
+    id integer NOT NULL PRIMARY KEY,
+    name varchar(255) NOT NULL,
+    age integer NULL
+);
+
+CREATE TABLE posts (
+    id integer NOT NULL PRIMARY KEY,
+    user_id integer NOT NULL
+);
+
+-- name: Only :one
+SELECT sqlc.embed(users) FROM users;
+
+-- name: WithAlias :one
+SELECT sqlc.embed(u) FROM users u;
+
+-- name: WithSubquery :many
+SELECT sqlc.embed(users), (SELECT count(*) FROM users) AS total_count FROM users;
+
+-- name: WithAsterisk :one
+SELECT sqlc.embed(users), * FROM users;
+
+-- name: Duplicate :one
+SELECT sqlc.embed(users), sqlc.embed(users) FROM users;
+
+-- name: Join :one
+SELECT sqlc.embed(users), sqlc.embed(posts) FROM posts
+INNER JOIN users ON posts.user_id = users.id;

internal/endtoend/testdata/sqlc_embed/mysql/sqlc.json

@@ -0,0 +1,12 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "engine": "mysql",
+      "name": "querytest",
+      "schema": "query.sql",
+      "queries": "query.sql"
+    }
+  ]
+}