MDL-81521 core: Update all possibly data providers to be static

Note: Some data providers could not be automatically be converted to
being static. These will be handled in a separate issue.

lib/xapi/tests/external/post_statement_test.php

@@ -187,7 +187,7 @@ class post_statement_test extends externallib_advanced_testcase {
      *
      * @return  array
      */
-    public function components_provider() : array {
+    public static function components_provider(): array {
         return [
             'Inexistent component' => [
                 'inexistent_component', []
@@ -233,7 +233,7 @@ class post_statement_test extends externallib_advanced_testcase {
      *
      * @return  array
      */
-    public function invalid_json_provider() : array {
+    public static function invalid_json_provider(): array {
         return [
             'Wrong json' => [
                 'This is not { a json object /'
@@ -376,7 +376,7 @@ class post_statement_test extends externallib_advanced_testcase {
      *
      * @return  array
      */
-    public function statement_provider() : array {
+    public static function statement_provider(): array {
         return [
             // Single statement with group statements enabled.
             'Single, Valid actor, valid verb' => [
@@ -449,7 +449,7 @@ class post_statement_test extends externallib_advanced_testcase {
      *
      * @return  array
      */
-    public function group_statement_provider() : array {
+    public static function group_statement_provider(): array {
         return [
             // Single statement with group statements enabled.
             'Group statement + group statement without group support' => [