feat: add PKCE support for OAuth2 Authorization Code flows (#5361)

* Add PKCE support.

* Fix tests

* Update oauth2.md

* Rename usePkce

* Fix the BrokenComponent error

* Update oauth2.md

* Remove isCode variable. Remove uuid4 dependency.

* Remove utils functions

* Import crypto

* Fix tests

* Fix the tests

* Cleanup

* Fix code_challenge generation

* Move code challenge and verifier to utils for mocks. Update tests.

* Mock the PKCE methods in the utils file properly.

* Add missing expect

* use target-method spies

* Add comments to explain test values.

* Get rid of jsrsasign.

test/mocha/core/system/system.jsx

@@ -916,8 +916,8 @@ describe("bound system", function(){
     describe("components", function() {
       it("should catch errors thrown inside of React Component Class render methods", function() {
         // Given
-        // eslint-disable-next-line react/require-render-return
         class BrokenComponent extends React.Component {
+          // eslint-disable-next-line react/require-render-return
           render() {
             throw new Error("This component is broken")
           }
@@ -943,8 +943,8 @@ describe("bound system", function(){
 
       it("should catch errors thrown inside of pure component render methods", function() {
         // Given
-        // eslint-disable-next-line react/require-render-return
         class BrokenComponent extends PureComponent {
+          // eslint-disable-next-line react/require-render-return
           render() {
             throw new Error("This component is broken")
           }
@@ -994,8 +994,8 @@ describe("bound system", function(){
 
       it("should catch errors thrown inside of container components", function() {
         // Given
-        // eslint-disable-next-line react/require-render-return
         class BrokenComponent extends React.Component {
+          // eslint-disable-next-line react/require-render-return
           render() {
             throw new Error("This component is broken")
           }