MDL-84694 theme: Replace legacy BS4 references in activities overview

Author: sarjona

course/format/templates/local/overview/activityname.mustache

@@ -37,7 +37,7 @@
         {{sectiontitle}}
     </div>
     {{/sectiontitle}}
-    <div class="ml-2">
+    <div class="ms-2">
         {{#hidden}}
         <span class="badge rounded-pill text-bg-secondary fw-normal">
             {{#pix}}i/show, core{{/pix}}

lib/templates/local/collapsable_section.mustache

@@ -84,7 +84,7 @@
                 >
                     <span class="dir-rtl-hide">{{#pix}} t/collapsedchevron, core {{/pix}}</span>
                     <span class="dir-ltr-hide">{{#pix}} t/collapsedchevron_rtl, core {{/pix}}</span>
-                    <span class="sr-only">{{!
+                    <span class="visually-hidden">{{!
                         }}{{$ expandlabel }}{{!
                             }}{{#expandlabel}}{{expandlabel}}{{/expandlabel}}{{!
                             }}{{^expandlabel}}{{#str}} expand, core {{/str}}{{/expandlabel}}{{!
@@ -101,7 +101,7 @@
                     }}"
                 >
                     {{#pix}} t/expandedchevron, core {{/pix}}
-                    <span class="sr-only">{{!
+                    <span class="visually-hidden">{{!
                         }}{{$ collapselabel }}{{!
                             }}{{#collapselabel}}{{collapselabel}}{{/collapselabel}}{{!
                             }}{{^collapselabel}}{{#str}} collapse, core {{/str}}{{/collapselabel}}{{!