make ForceNew on newly added required field

.changelog/5362.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+bigquery: fixed a bug of cannot add required fields to an existing schema on `google_bigquery_table`
+```

google/resource_bigquery_table.go

@@ -225,6 +225,17 @@ func resourceBigQueryTableSchemaIsChangeable(old, new interface{}) (bool, error)
 			return false, err
 		}
 		mapNew := bigQueryArrayToMapIndexedByName(arrayNew)
+		for key := range mapNew {
+			// making unchangeable if an newly added column is with REQUIRED mode
+			if _, ok := mapOld[key]; !ok {
+				items := mapNew[key].(map[string]interface{})
+				for k := range items {
+					if k == "mode" && fmt.Sprintf("%v", items[k]) == "REQUIRED" {
+						return false, nil
+					}
+				}
+			}
+		}
 		for key := range mapOld {
 			// all old keys should be represented in the new config
 			if _, ok := mapNew[key]; !ok {

google/resource_container_node_pool.go

@@ -1,13 +1,13 @@
 package google
 
 import (
-	"context"
 	"fmt"
 	"log"
 	"regexp"
 	"strings"
 	"time"
 
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/customdiff"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/resource"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/validation"