Othographic camera in-editor now uses Z near/far settings instead of a hardcoded value

Fixes #18809.

The in-editor ortho camera used a far clipping plane of 8192 units, and was
placed 4096 units away from the camera cursor.

This was far enough to cause culling issues from floating point precision loss
on objects smaller than one unit.

This change modifies the near/far clipping planes of the ortho camera to use
those specified in the editor (and currently used by the perspective camera).
The frustum is still centered around the camera cursor location, as it was
before.

(cherry picked from commit 26912c15e625f234a0528f239bf5e5ab2f858d9a)

editor/plugins/node_3d_editor_plugin.cpp

@@ -347,7 +347,7 @@ void Node3DEditorViewport::_update_camera(float p_interp_delta) {
 		if (orthogonal) {
 			float half_fov = Math::deg2rad(get_fov()) / 2.0;
 			float height = 2.0 * cursor.distance * Math::tan(half_fov);
-			camera->set_orthogonal(height, 0.1, 8192);
+			camera->set_orthogonal(height, get_znear(), get_zfar());
 		} else {
 			camera->set_perspective(get_fov(), get_znear(), get_zfar());
 		}
@@ -364,7 +364,7 @@ Transform Node3DEditorViewport::to_camera_transform(const Cursor &p_cursor) cons
 	camera_transform.basis.rotate(Vector3(0, 1, 0), -p_cursor.y_rot);
 
 	if (orthogonal)
-		camera_transform.translate(0, 0, 4096);
+		camera_transform.translate(0, 0, (get_zfar() - get_znear()) / 2.0);
 	else
 		camera_transform.translate(0, 0, p_cursor.distance);