Refine the colors of some more components (#12343)

* Refine the colors of some more components

This is a reintroduction of https://github.com/matrix-org/matrix-react-sdk/pull/12255, and should be the last part of the Compound color refinement work (https://github.com/element-hq/element-web/issues/26992). I've updated the following components to reflect design decisions (https://www.figma.com/file/pqhlirZFEwEp5XpudSbiia/Theming-Web-templates?type=design&node-id=80-60219&mode=design&t=mjqwylUie1vRwzOV-0) that will help them fit in better with the new design system:

- Message bubbles
- Pills
- Sent indicators
- Jump to bottom/unread buttons
- Composer placeholder
- Notification badges
- Room sublists
- Verification shields
- Date separators
- Tooltips

Closes https://github.com/element-hq/element-web/issues/22122

* Update some screenshots

res/css/views/messages/_DateSeparator.pcss

@@ -39,5 +39,5 @@ limitations under the License.
     mask-size: contain;
     mask-repeat: no-repeat;
     mask-image: url("$(res)/img/feather-customised/chevron-down.svg");
-    background-color: $tertiary-content;
+    background-color: var(--cpd-color-icon-secondary);
 }

res/css/views/messages/_TimelineSeparator.pcss

@@ -20,12 +20,12 @@ limitations under the License.
     display: flex;
     align-items: center;
     font: var(--cpd-font-body-md-regular);
-    color: $roomtopic-color;
+    color: var(--cpd-color-text-secondary);
 }
 
 .mx_TimelineSeparator > hr {
     flex: 1 1 0;
     height: 0;
     border: none;
-    border-bottom: 1px solid $menu-selected-color;
+    border-bottom: 1px solid var(--cpd-color-gray-400);
 }