table-of-contents: avoid action helper

Let's avoid using the `action` helper and instead prefer to use the `on`
and `fn` helpers together. These new helpers have more clearly
delineated responsibilities, which should make the operations a little
bit easier to understand.

Author: geneukum

app/components/table-of-contents.hbs

@@ -1,6 +1,6 @@
 <ol class='toc-level-0'>
   <li class='toc-level-0'>
-    <a {{action 'toggle' 'modules'}} href='#' data-test-toc-title='packages'>Packages</a>
+    <a {{on 'click' (fn this.toggle 'modules')}} href='#' data-test-toc-title='packages'>Packages</a>
     <ol class='toc-level-1 modules selected'>
       {{#each @moduleIDs as |moduleID|}}
 
@@ -16,7 +16,7 @@
 
   {{#if @isShowingNamespaces}}
     <li class='toc-level-0'>
-      <a {{action 'toggle' 'namespaces'}} href='#' data-test-toc-title='namespaces'>Namespaces</a>
+      <a {{on 'click' (fn this.toggle 'namespaces')}} href='#' data-test-toc-title='namespaces'>Namespaces</a>
       <ol class='toc-level-1 namespaces selected'>
         {{#each @namespaceIDs as |namespaceID|}}
           <li class='toc-level-1' data-test-namespace={{namespaceID}}>
@@ -28,7 +28,7 @@
   {{/if}}
 
   <li class='toc-level-0'>
-    <a {{action 'toggle' 'classes'}} href='#' data-test-toc-title='classes'>Classes</a>
+    <a {{on 'click' (fn this.toggle 'classes')}} href='#' data-test-toc-title='classes'>Classes</a>
     <ol class='toc-level-1 classes selected'>
       {{#each @classesIDs as |classID|}}
         <li class='toc-level-1' data-test-class={{classID}}>