Render timeline separator for late event groups (#11739)

* Use Compound tooltips on MessageTimestamp to improve UX of date time discovery

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Show io.element.late_event in MessageTimestamp when known

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Update snapshot

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Avoid needing new Compound changes

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Move groupers into their own directory

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Refactor date separator code to be more generic

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Render timeline separator for late event groups

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Fix date used in copy

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Update snapshot

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Move groupers into their own directory

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Update copy

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Update copy

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Update snapshot

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* i18n

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Add comments

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Add comments

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

---------

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

test/components/structures/__snapshots__/MessagePanel-test.tsx.snap

@@ -40,7 +40,7 @@ exports[`MessagePanel should handle lots of membership events quickly 1`] = `
         >
           <div
             aria-label="Thu, Jan 1, 1970"
-            class="mx_DateSeparator"
+            class="mx_TimelineSeparator"
             role="separator"
           >
             <hr