Convert file_element_info() to Element classes

Working on this

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

file_managed_file_validate() was used in one other place.

+++ b/core/modules/file/src/Element/ManagedFile.php
@@ -0,0 +1,350 @@
+            if ($file = file_load($fid)) {

We can use static method here.

Okay

Duh! We need to specify the #value_callback until its a proper callback.

If you disagree with 1 and 2 it's fine by me perhaps we can add @todo (with issue id) for those methods.

1. +++ b/core/modules/file/src/Element/ManagedFile.php
   @@ -0,0 +1,348 @@
   +      if ($files = file_managed_file_save_upload($element, $form_state)) {
   

   IMO we can also move this function here.

2. +++ b/core/modules/file/src/Element/ManagedFile.php
   @@ -0,0 +1,348 @@
   +      '#submit' => ['file_managed_file_submit'],
   ...
   +      '#submit' => ['file_managed_file_submit'],
   

   IMO we have to move this function as well to this element file. Right know we are not using it at anyplace other then this.

3. +++ b/core/modules/file/src/Element/ManagedFile.php
   @@ -0,0 +1,348 @@
   +      $element['upload_button']['#ajax']['progress']['path'] = 'file/progress/' . $upload_progress_key;
   

   Can't we use controller/routes here?

4. +++ b/core/modules/file/src/Element/ManagedFile.php
   @@ -0,0 +1,348 @@
   +   * of in file_managed_file_process(), because #access for these buttons
   ...
   +   * form_builder() for more detailed information about the relationship between
   

   Minor doc update file_managed_file_process doesn't exist anymore and from_builder is deprecated. There is one more ref to file_managed_file_process just above file_managed_file_submit we have to update that as well.

This should resolve #17.4.

+++ b/core/modules/file/file.module
@@ -52,14 +52,22 @@ function file_help($route_name, RouteMatchInterface $route_match) {
+ * @todo Remove once https://www.drupal.org/node/2326409 is in.

this issue is in so needs reroll.

Thank you married guy :D

Committed 69be11e and pushed to 8.0.x. Thanks!