[5.x] Add Nav & Collection Tree Saving events

[ryanmitchell]

Someone was looking for NavTreeSaving and CollectionTreeSaving in discussions earlier: #10618

This PR adds them.

Closes statamic/ideas#1207.

[wuifdesign]

i think you are missing the changes to handle the false state.

// CollectionTreeController.php
$saved = $tree->tree($contents)->save();

return [
  'saved' => $saved,
];

something like:

// PageTree.vue
if (! response.data.saved) {
  return this.$toast.error(__(`Couldn't save tree`));
}

and return true at the end of the save function in the Tree.php

same changes for the delete part.

[wuifdesign]

changes looks good :)

no idea but is this change also needed for delete? And also for NavTree to work correctly with NavTree Events?

[ryanmitchell]

Deleting in the CP only happens by deleting the whole nav, so it shouldn't need UI.

[jasonvarga]

Do you really need the Deleting events at the moment?

This can prevent the tree from being deleted, but that doesn't stop the nav from being deleted.

[ryanmitchell]

Nope. Dump them if they are causingproblems.