Adapt OAuth2 implementation to Matrix Spec v1.18 (#34026)

* Adapt OAuth2 implementation to Matrix Spec v1.18

* Handle more cases of oidc->oauth

* Fix test

* Fix read back of oauth2 context

* Iterate

* Fix tests

* Discard changes to apps/web/playwright/e2e/settings/account-user-settings-tab.spec.ts

* Fix test

* Fix test

* Fix test

* Potential fix for pull request finding 'Unused variable, import, function or class'

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* Iterate

* Iterate

* Fix test

---------

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apps/desktop/playwright/e2e/launch/oidc.spec.ts

@@ -9,7 +9,7 @@ import { test, expect } from "../../element-desktop-test.js";
 
 declare global {
     interface ElectronPlatform {
-        getOidcCallbackUrl(): URL;
+        getOAuthCallbackUrl(): URL;
     }
 
     interface Window {
@@ -29,7 +29,7 @@ test.describe("OIDC Native", () => {
     test("should use OIDC callback URL without authority component", async ({ page }) => {
         await expect(
             page.evaluate<string>(() => {
-                return window.mxPlatformPeg.get().getOidcCallbackUrl().toString();
+                return window.mxPlatformPeg.get().getOAuthCallbackUrl().toString();
             }),
         ).resolves.toMatch(/io\.element\.(desktop|nightly):\/vector\/webapp\//);
     });