MDL-64267 core_message: sticky positioning of contact request info

message/templates/message_drawer_view_conversation_body.mustache

@@ -44,7 +44,7 @@
 >
     <div class="position-relative h-100" data-region="content-container" style="overflow-y: auto; overflow-x: hidden">
         <div class="content-message-container hidden h-100 px-2 pt-0" data-region="content-message-container" role="log" style="overflow-y: auto; overflow-x: hidden">
-            <div class="p-3 text-center hidden" data-region="contact-request-sent-message-container">
+            <div class="py-3 bg-light position-sticky border-bottom text-center hidden" data-region="contact-request-sent-message-container" style="top: 0">
                 <p class="m-0">{{#str}} contactrequestsent, core_message {{/str}}</p>
                 <p class="font-italic font-weight-light" data-region="text"></p>
             </div>

theme/bootstrapbase/less/moodle/bs4-compat.less

@@ -562,6 +562,9 @@
 .position-relative {
     position: relative !important;
 }
+.position-sticky {
+    position: sticky !important;
+}
 .align-self-start {
     align-self: flex-start !important;
 }

theme/bootstrapbase/style/moodle.css

@@ -22338,6 +22338,9 @@ ul.indented-list {
 .position-relative {
   position: relative !important;
 }
+.position-sticky {
+  position: sticky !important;
+}
 .align-self-start {
   align-self: flex-start !important;
 }