Fixes #12127 - sets z-index on block list actions element (#13179)

* Sets z-index on block list actions element

Should solve #12127 https://github.com/umbraco/Umbraco-CMS/issues/12127

* #12127 : introduces variable for block actions z-index

src/Umbraco.Web.UI.Client/src/less/variables.less

@@ -353,6 +353,7 @@
 // Try to avoid customizing these :)
 @zIndexEditor: 100;
 @zIndexTree: 100;
+@zIndexBlockActions: 500;
 @zindexDropdown: 1000;
 @zindexPopover: 1010;
 @zindexTooltip: 1030;

src/Umbraco.Web.UI.Client/src/views/propertyeditors/blocklist/umb-block-list-property-editor.less

@@ -86,6 +86,7 @@ ng-form.ng-invalid-val-server-match-settings > .umb-block-list__block > .umb-blo
     border-radius: 16px;
     padding-left: 5px;
     padding-right: 5px;
+    z-index: @zIndexBlockActions;
     .action {
         position: relative;
         display: inline-block;