New theme ui in user settings (#12576)
* Add hook to get the theme
* Adapt subsection settings to new ui
* WIP new theme subsection
* Add theme selection
* Fix test types
* Disabled theme selector when system theme is used
* Update compound to `4.4.1`
* Add custom theme support
* Remove old ThemChoicePanel
* Fix QuickThemeSwitcher-test.tsx
* Fix AppearanceUserSettingsTab-test.tsx
* Update i18n
* Fix ThemeChoicePanel-test.tsx
* Update `@vector-im/compound-web`
* Small tweaks
* Fix CSS comments and use compound variable
* Remove custom theme title
* i18n: update
* test: add tests to theme selection
* test: update AppearanceUserSettingsTab-test snapshot
* test: rework custom theme
* playwright: fix audio-player.spec.ts
* playwright: appearance tab
* test: update snapshot
* playright: add custom theme
* i18n: use correct char for ellipsis
* a11y: add missing aria-label to delete button
* dialog: update close button tooltip
* theme: remove local state and handle custom delete
* theme: don't add twice the same custom theme
* test: update snapshot
* playwright: update snapshot
* custom theme: add background to custom theme list
* update compound web
* Use new destructive property on `IconButton` of theme panel
* test: update snapshots
* rename new ui into legacy
* remove wrong constructor doc
* fix theme selector padding
* theme selector: fix key
* test: fix e2e
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