Remove most EditorNode constructor parameters and fields

[trollodel]

Follow up of #55066

Remove most EditorNode parameters and class attributes.
The only missing EditorNode references are:

• EditorScript.
• Plugins registered with EditorPlugins::add_by_type (only in some modules).
  Any reference to the given parameter is gone, and they were renamed to _p_editor.
• EditorPlugins::creator, because, is a more important change that deserves its PR.

In some cases, I create local variables to shorten lines (since EditorNode::get_singleton() it's bigger than editor).

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This PR has tons of changed files, Here's a summary of the changes to them:

• InspectorDock, FileSystemDock, SceneTreeDock, CanvasItemEditor, Node3DEditor and related classes has notable changes due to several usages of EditorNode.
• Some classes had from 1 to 4 usages of EditorNode.
• Some classes use EditorNode only in the constructor and in the make_visible method (if it's a bottom panel plugin).
• Some classes use EditorNode only in the constructor by calling EditorNode::add_bottom_panel_item.
• Few classes don't use EditorNode at all.
• AbstractPolygon2DEditor and subclasses no longer has the EditorNode parameter,
• Module's editor plugins no longer use the EditorNode parameter, and that parameter was renamed from p_editor to _p_editor.
• Removed the EditorNode reference in all headers (excluding EditorScript).

---

This PR increases the EditorNode::get_singleton usages, as expected.
In many cases, it's possible to use the EditorPlugin methods instead (which use EditorNode, but that's an implementation detail).
It will be done in a follow-up PR.

EditorNode::get_singleton usages in master (1894f3f):

rg "EditorNode::get_singleton()" | wc -l
745

EditorNode::get_singleton usages in this PR:

rg "EditorNode::get_singleton()" | wc -l
996

CC @KoBeWi

[akien-mga]

I like the idea. I've actually be poking at improving some include dependencies in editor following #57641, and there indeed plenty of unnecessary editor_node.h includes in headers due to this (and sometimes unnecessary dependencies in the .cpp too for plugins which don't actually need EditorNode at all).

akien-mga@7b724cd

There's a handful of plugins changed in the above commit to forward declare EditorNode but this becomes unnecessary after this PR.

[trollodel]

Once I'll migrate editor classes to use EditorPlugin and I'll remove the EditorNode usages in "editor_plugin.h", most editor classes won't need to interact (directly) with EditorNode at all.

[akien-mga]

Thanks!

[KoBeWi]

There is an unnecessary EditorNode forward declaration further up. If you are removing editor variable, you should also remove all EditorNode references that aren't necessary anymore. There might be some unused includes now too.

[trollodel]

Agree, but this is not the last cleanup PR I will do :)

There might be some unused includes now too.

Unused probably not. But some that can be moved to the .cpp? Surely yes!

[KoBeWi]

I was still reviewing this .-.
But well, it's fine overall, there are just some leftover like I commented above.