feat(HXDisclosureElement): add declarative functionality

* Rename private `_toggle()` to public `click()`
* Refactor source code to use `$` API from HXElement
* Update internal method names to closer adhere to best practices

Author: Ryan A. Johnson

docs/elements/hx-disclosure/index.html

@@ -41,6 +41,14 @@ <h2 id="target-element">Target Element</h2>
       </li>
     </ol>
   </section>
+
+  <section>
+    <h2 id="methods">Methods</h2>
+    <dl>
+      <dt>click()</dt>
+      <dd>Simulates a mouse click on the element</dd>
+    </dl>
+  </section>
 {% endblock %}
 
 {% block attributes %}

src/helix-ui/elements/HXDisclosureElement.js

@@ -33,15 +33,15 @@ export class HXDisclosureElement extends HXElement {
             this.expanded = false;
         }
 
-        this.addEventListener('click', this._toggle);
+        this.addEventListener('click', this._onClick);
         this.addEventListener('keydown', this.$preventScroll);
-        this.addEventListener('keyup', this._keyUp);
+        this.addEventListener('keyup', this._onKeyUp);
     }
 
     $onDisconnect () {
-        this.removeEventListener('click', this._toggle);
+        this.removeEventListener('click', this._onClick);
         this.removeEventListener('keydown', this.$preventScroll);
-        this.removeEventListener('keyup', this._keyUp);
+        this.removeEventListener('keyup', this._onKeyUp);
 
         if (this.target) {
             this.target.removeEventListener('open', this._onTargetOpen);
@@ -87,25 +87,27 @@ export class HXDisclosureElement extends HXElement {
         return this._target;
     }
 
+    /**
+     * Simulates mouse click
+     */
+    click () {
+        if (!this.disabled) {
+            this.expanded = !this.expanded;
+        }
+    }
+
     /** @private */
-    _keyUp (event) {
+    _onKeyUp (event) {
         switch (event.keyCode) {
             case KEYS.Space:
             case KEYS.Enter:
-                this._toggle();
+                this.click();
                 break;
             default:
                 break;
         }
     }
 
-    /** @private */
-    _toggle () {
-        if (!this.disabled) {
-            this.expanded = !this.expanded;
-        }
-    }
-
     /** @private */
     _onTargetOpen () {
         this.expanded = true;
@@ -115,4 +117,9 @@ export class HXDisclosureElement extends HXElement {
     _onTargetClose () {
         this.expanded = false;
     }
+
+    /** @private */
+    _onClick () {
+        this.click();
+    }
 }