MDL-64820 forum: change disucssion subscribe back to link

Changed the discussion subscribe button back to a link because
it was breaking all of the behat tests.

mod/forum/classes/local/exporters/discussion.php

@@ -115,6 +115,7 @@ class discussion extends exporter {
                         'type' => PARAM_URL,
                     ],
                     'markasread' => ['type' => PARAM_URL],
+                    'subscribe' => ['type' => PARAM_URL]
                 ],
             ]
         ];
@@ -182,6 +183,7 @@ class discussion extends exporter {
                 'view' => $urlfactory->get_discussion_view_url_from_discussion($discussion)->out(false),
                 'viewfirstunread' => $viewfirstunreadurl->out(false),
                 'markasread' => $urlfactory->get_mark_discussion_as_read_url_from_discussion($forum, $discussion)->out(false),
+                'subscribe' => $urlfactory->get_discussion_subscribe_url($discussion)->out(false)
             ]
         ];
 

mod/forum/classes/local/factories/url.php

@@ -443,4 +443,18 @@ class url {
             'return' => $this->get_forum_view_url_from_forum($forum)->out(),
         ]);
     }
+
+    /**
+     * Get the url to subscribe to a discussion.
+     *
+     * @param discussion_entity $discussion The discussion
+     * @return moodle_url
+     */
+    public function get_discussion_subscribe_url(discussion_entity $discussion) : moodle_url {
+        return new moodle_url('/mod/forum/subscribe.php', [
+            'sesskey' => sesskey(),
+            'id' => $discussion->get_forum_id(),
+            'd' => $discussion->get_id()
+        ]);
+    }
 }

mod/forum/templates/discussion_subscription_toggle.mustache

@@ -33,16 +33,19 @@
     }
 }}
 {{#capabilities.subscribe}}
-    <button
+    <a
+        href="{{{urls.subscribe}}}"
         class="p-3 btn btn-link"
         data-type="subscription-toggle"
         data-action="toggle"
         data-discussionid="{{id}}"
         data-forumid="{{forumid}}"
         {{#userstate.subscribed}}
+            title="{{#str}}clicktounsubscribe, mod_forum{{/str}}"
             data-targetstate="0"
         {{/userstate.subscribed}}
         {{^userstate.subscribed}}
+            title="{{#str}}clicktosubscribe, mod_forum{{/str}}"
             data-targetstate="1"
         {{/userstate.subscribed}}
     >
@@ -52,5 +55,5 @@
         {{^userstate.subscribed}}
             {{#pix}}t/unsubscribed, mod_forum, {{#str}}clicktosubscribe, mod_forum{{/str}}{{/pix}}
         {{/userstate.subscribed}}
-    </button>
+    </a>
 {{/capabilities.subscribe}}