Allow user to set timezone (#12775)

...wright/e2e/settings/preferences-user-settings-tab.spec.ts

...user-settings-tab-should-be-rendered-properly-1-linux.png

...components/views/settings/shared/_SettingsSubsection.pcss

src/DateUtils.ts

src/TimezoneHandler.ts

src/components/structures/RoomView.tsx

...s/views/settings/tabs/user/PreferencesUserSettingsTab.tsx

src/contexts/RoomContext.ts

src/i18n/strings/en_EN.json

src/settings/Settings.tsx

test/TimezoneHandler-test.ts

test/components/views/rooms/SendMessageComposer-test.tsx

...ws/settings/tabs/user/PreferencesUserSettingsTab-test.tsx

...er/__snapshots__/PreferencesUserSettingsTab-test.tsx.snap

test/test-utils/room.ts