Convert contextual_element_info() into Element classes

1. +++ b/core/modules/contextual/src/Element/ContextualLinks.php
   @@ -0,0 +1,108 @@
   +class ContextualLinks extends FormElement {
   +  /**
   ...
   +  }
   +}
   
   +++ b/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php
   @@ -0,0 +1,52 @@
   +class ContextualLinksPlaceholder extends FormElement {
   +  /**
   ...
   +  }
   +}
   

   Please include a blank line at the beginning and end of the class

2. +++ b/core/modules/contextual/src/Element/ContextualLinks.php
   @@ -0,0 +1,108 @@
   +   * @param $element
   ...
   +   * @return
   
   +++ b/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php
   @@ -0,0 +1,52 @@
   +   * @param $element
   ...
   +   * @return
   

   These should be typehinted with array

3. +++ b/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php
   @@ -0,0 +1,52 @@
   +   * @see contextual_element_info()
   

   You just removed this, don't @see it :)

Ah, I didn't notice that. Yes, if they don't have #input => TRUE, they are RenderElements.

+++ b/core/modules/contextual/src/Element/ContextualLinks.php
@@ -7,14 +7,14 @@
  * @FormElement("contextual_links")

+++ b/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php
@@ -8,14 +8,14 @@
  * @FormElement("contextual_links_placeholder")

Please also change the annotation. Thanks!

Excellent work @almaudoh! If this weren't horribly blocked by #2326409: Annotate render element plugins, it'd be RTBC.

Rerolled for now without the hook_element_info() removal in light of #2326409: Annotate render element plugins

NW for #2.

1. +++ b/core/modules/contextual/src/Element/ContextualLinks.php
   @@ -0,0 +1,111 @@
   + * @todo Annotate once https://www.drupal.org/node/2326409 is in.
   

   I'd love to see this issue get fixed.

2. +++ b/core/modules/contextual/src/Element/ContextualLinks.php
   @@ -0,0 +1,111 @@
   +    return \Drupal::service('plugin.manager.menu.contextual_link');
   

   I thought we can inject these but @tim.plunkett gave some valid points in irc and I think it needs little more discussion. So NW for this sorry.

3. +++ b/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php
   @@ -0,0 +1,54 @@
   +   * Renders an empty (hence invisible) placeholder div with a data-attribute that
   +   * contains an identifier ("contextual id"), which allows the JavaScript of the
   

   More then 80 chars.

Thank you @tim.plunkett for fixing the issues.

+++ b/core/modules/contextual/src/Element/ContextualLinks.php
@@ -0,0 +1,120 @@
+      $class = drupal_html_class($class);

We can use Html::getClass($class); here.

Other then this we this is done so RTBC.

Committed and pushed to 8.x. Thanks!