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'

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

* Iterate

* Iterate

* Fix test

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apps/web/test/unit-tests/components/views/spaces/SpacePanel-test.tsx

@@ -123,6 +123,7 @@ describe("<SpacePanel />", () => {
         removeListener: jest.fn(),
         isVersionSupported: jest.fn().mockResolvedValue(true),
         doesServerSupportUnstableFeature: jest.fn().mockResolvedValue(false),
+        getAuthMetadata: jest.fn().mockRejectedValue(new Error("Legacy auth")),
     } as unknown as MatrixClient;
     const sdkContext = new TestSDKContext();
     const SpacePanel = wrapInSdkContext(wrapInMatrixClientContext(UnwrappedSpacePanel), sdkContext);