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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pnpm-workspace.yaml

@@ -114,8 +114,6 @@ overrides:
     pretty-format@30>react-is: 19.2.6
     "@types/react": "catalog:"
     "@types/react-dom": "catalog:"
-    oidc-client-ts: 3.5.0
-    jwt-decode: 4.0.0
     caniuse-lite: 1.0.30001799
     markdown-it: 14.1.1
     matrix-widget-api: "^1.17.0"