MDL-42796 ActionMenu: Add additional keyboard event handling

Add additional handling for up/down/escape key presses and consolidate them
with the existing tab/shift+tab handling.

theme/base/style/core.css

@@ -1575,8 +1575,7 @@ img#persona_signin { cursor: pointer; }
     width: 12px;
     height: 12px;
 }
-.moodle-actionmenu[data-enhanced].show .menu a:hover,
-.moodle-actionmenu[data-enhanced].show .menu a:focus {color: #ffffff;background-color: #0088cc;}
+.moodle-actionmenu[data-enhanced].show .menu a:hover {color: #ffffff;background-color: #0088cc;}
 .moodle-actionmenu[data-enhanced].show .menu a:first-child {-webkit-border-top-right-radius: 4px;border-top-right-radius: 4px;-webkit-border-top-left-radius: 4px;border-top-left-radius: 4px;-moz-border-radius-topright: 4px;-moz-border-radius-topleft: 4px;}
 .moodle-actionmenu[data-enhanced].show .menu a:last-child {-webkit-border-bottom-right-radius: 4px;border-bottom-right-radius: 4px;-webkit-border-bottom-left-radius: 4px;border-bottom-left-radius: 4px;-moz-border-radius-bottomright: 4px;-moz-border-radius-bottomleft: 4px;}
 .moodle-actionmenu[data-enhanced].show .menu a.hidden {display: none;}

theme/bootstrapbase/less/moodle/core.less

@@ -2060,8 +2060,7 @@ img#persona_signin {
             display: block;
             color: @dropdownLinkColor;
             padding:2px 1em 2px 28px;
-            &:hover,
-            &:focus {
+            &:hover {
                 color: @dropdownLinkColorHover;
                 background-color: @dropdownLinkBackgroundHover;
             }