entc/gen/template/dialect/sql: cleaning up isSQLConstraintError (#1319)

* entc/gen/template/dialect/sql: cleaning up isSQLConstraintError in generated ent.go to use new sqlgraph IsConstraintError checks.

Adding IsFK and IsUniqueness methods to the generated ent.ConstraintError (on SQL dialects) struct to allow users to glean more information about the specific constraint violation.

Fixes #1310

* fix indentation in tmpl file
regen files
rm new methods from generated code

* regen

examples/m2m2types/ent/ent.go

@@ -9,7 +9,6 @@ package ent
 import (
 	"errors"
 	"fmt"
-	"strings"
 
 	"entgo.io/ent"
 	"entgo.io/ent/dialect"
@@ -242,22 +241,8 @@ func IsConstraintError(err error) bool {
 }
 
 func isSQLConstraintError(err error) (*ConstraintError, bool) {
-	var (
-		msg = err.Error()
-		// error format per dialect.
-		errors = [...]string{
-			"Error 1062",               // MySQL 1062 error (ER_DUP_ENTRY).
-			"UNIQUE constraint failed", // SQLite.
-			"duplicate key value violates unique constraint", // PostgreSQL.
-		}
-	)
-	if _, ok := err.(*sqlgraph.ConstraintError); ok {
-		return &ConstraintError{msg, err}, true
-	}
-	for i := range errors {
-		if strings.Contains(msg, errors[i]) {
-			return &ConstraintError{msg, err}, true
-		}
+	if sqlgraph.IsConstraintError(err) {
+		return &ConstraintError{err.Error(), err}, true
 	}
 	return nil, false
 }