Change ComponentSourceInterface::preSaveItem($item) to ::optimizeExplicitInput($values)

Overview

:thinking: Why `ComponentTreeItem` and not just `ComponentInputs`? This means that _more_ than just the inputs can be modified by a `ComponentSource` plugin, which I think is a huge risk when we make this a public API.

IMHO this should be changed to something like:
```suggestion:-9+0
  public function optimizeExplicitInput(array $inputValues): void;
```

which removes that risk entirely. Note that `::getDefaultExplicitInput()` already returns such an array, and `::validateComponentInput()` already accepts such an array. So it seems more consistent, too.

Won't block this commit on it though, because `ComponentSourceInterface` won't be a public API until 1.0. :thumbsup:

— https://git.drupalcode.org/project/experience_builder/-/merge_requests/1...

public function preSaveItem(ComponentTreeItem $item): void;
public function optimizeExplicitInput(array $inputValues): voi

Proposed resolution

User interface changes