feat: many2many relations check

tests/testdata/src/relations_check/positive.go

@@ -0,0 +1,21 @@
+package relations_check
+
+type Student struct {
+	Id      uint     `gorm:"primaryKey"`
+	Courses []Course `gorm:"many2many:student_courses;"`
+}
+
+type Course struct {
+	Id       uint     `gorm:"primaryKey"`
+	Students []Course `gorm:"many2many:student_courses;"` // want "Invalid type `Course` in M2M relation \\(use \\[\\]\\*Student or self-reference\\)"
+}
+
+type Author struct {
+	Id       uint      `gorm:"primaryKey"`
+	Articles []Article `gorm:"many2many:author_articles;"`
+}
+
+type Article struct {
+	Id      uint   `gorm:"primaryKey"`
+	Authors Author `gorm:"many2many:author_articles;"` // want "M2M relation `author_articles` with bad type `Author` \\(should be a slice\\)"
+}