Convert confirm_form() in path.admin.inc to the new form interface

"Having a crack" as they say here.

First shot at the conversion.

#2: 1946444-convert-path-confirm-iface-2.patch queued for re-testing.

Wasn't loading the path alias correctly, which I'm now doing by injecting a Path crud object on the form and calling path->load().

Thanks to @timplunkett for the IRC help.

+++ b/core/modules/path/lib/Drupal/path/Form/DeleteForm.phpundefined
@@ -0,0 +1,91 @@
+  public function buildForm(array $form, array &$form_state, int $pid = NULL) {

You can't typehint with 'int', especially since it could be an int or string.

Removed type hinting per #8 and fixed some docs.

Looks good to me!

hmm shouldn't the cancel path be a route rather than a path?

Opened #1963394: ConfirmFormBase::getCancelPath() should allow for a route since this is a bit of a can of worms. Committed/pushed to 8.x.