Use Intl to localise dates and times (#11422)

* Use Intl to generate better internationalised date formats

* Get `Yesterday` and `Today` from Intl also

* Correct capitalisation blunder

* Fix formatTime include weekday

* Iterate

* Fix tests

* use jest setSystemTime

* Discard changes to cypress/e2e/settings/general-user-settings-tab.spec.ts

* Discard changes to res/css/_components.pcss

* Discard changes to res/css/views/elements/_LanguageDropdown.pcss

* Discard changes to src/components/views/elements/LanguageDropdown.tsx

* Add docs & tests for getDaysArray & getMonthsArray

* Discard changes to test/components/structures/__snapshots__/MatrixChat-test.tsx.snap

* Consolidate consts

* Improve testing & documentation

* Update snapshot

* Apply suggestions from code review

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* Iterate

* Clarify comments

* Update src/DateUtils.ts

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* Specify hourCycle

* Discard changes to test/components/views/settings/devices/DeviceDetails-test.tsx

* Update comments

---------

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

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

@@ -93,7 +93,7 @@ describe("SearchResultTile", () => {
                         room_id: ROOM_ID,
                         content: { body: `Message #${i}` },
                         event_id: `$${i}:server`,
-                        origin_server_ts: undefined,
+                        origin_server_ts: i,
                     }),
             ),
         });

test/components/views/rooms/__snapshots__/PinnedEventTile-test.tsx.snap

@@ -51,7 +51,7 @@ exports[`<PinnedEventTile /> should render pinned event 1`] = `
       <span
         class="mx_MessageTimestamp mx_PinnedEventTile_timestamp"
       >
-        Thu, Jan 1 1970 00:00:00
+        Thu, Jan 1, 1970, 00:00
       </span>
       <div
         class="mx_AccessibleButton mx_AccessibleButton_hasKind mx_AccessibleButton_kind_link"