entc/gen: add support for indexing id fields (#991)

* fix: allow indexes to be created on ID field

* test: add case for id field

* remove extraneous nil check

* change add primary method

* add integration test for mixin id

* go generate

* add default for default

* make linter happy

* invert if statement

* add default index to card integration test

* add index on default id, mixin id, and composite index

* go generate

dialect/sql/schema/schema.go

@@ -47,7 +47,7 @@ func NewTable(name string) *Table {
 
 // AddPrimary adds a new primary key to the table.
 func (t *Table) AddPrimary(c *Column) *Table {
-	t.Columns = append(t.Columns, c)
+	t.AddColumn(c)
 	t.PrimaryKey = append(t.PrimaryKey, c)
 	return t
 }