Implement new design for Welcome page (#33211)

* Convert welcome.html to React component

In advance of changes to use Compound

* Fix types

* Fix tests

* Update styling to match Figma

* Fix random capitalisation

* Tweak styling

* Regenerate i18n

* Update tests

* Make linter happy

* Iterate

.github/workflows/static_analysis.yaml

@@ -103,7 +103,7 @@ jobs:
                           voip|element_call
                           error|invalid_json
                           error|misconfigured
-                          welcome_to_element
+                          welcome|title_element
                           devtools|settings|elementCallUrl
                           labs|sliding_sync_description
                           settings|voip|noise_suppression_description