Select the last object of the group as the alignment target when using `Mobject.arrange()`

## Description of proposed feature


### My motivation

Hello, I want to be able to select the last object in a group as the target for alignment when using `Mobject.arrange()`, instead of the default first object.

Like this:

https://github.com/user-attachments/assets/abd9c835-6a4e-4182-be2c-b71372e7c2a9

### Why

`Mobject.arrange()` always uses the first object as the alignment target:

https://github.com/ManimCommunity/manim/blob/2ab99b53d3e8f43b1cd7245208d78c5dd6f9414a/manim/mobject/mobject.py#L2368-L2372

If I want to implement reverse-arrange, I must use the `Mobject.next_to()` method one by one (in reverse order) for the objects within the group, as implemented in above code.

## How can the new feature be used?


By adding a new param `last` in `Mobject.arrange()`:

```python
group.animate.arrange(center=False, last=True, direction=LEFT)
```

## Additional comments


Here is my change of `Mobject.arrange()` to implement this feature:

```python
def arrange(
    self,
    direction: Vector3D = RIGHT,
    buff: float = DEFAULT_MOBJECT_TO_MOBJECT_BUFFER,
    center: bool = True,
    last: bool = False,
    **kwargs,
) -> Self:
    if last:
        submobjects = list(reversed(self.submobjects))
    else:
        submobjects = self.submobjects
    
    for m1, m2 in zip(submobjects, submobjects[1:]):
        m2.next_to(m1, direction, buff, **kwargs)
    if center:
        self.center()
    return self
```

Here is my code to test this feature:

```python
from manim import *

class ReversedArrange(Scene):

    def construct(self):
        square_r = Square(fill_color=RED, fill_opacity=1).move_to(ORIGIN + LEFT * 5)
        square_g = Square(fill_color=GREEN, fill_opacity=1).move_to(ORIGIN)
        square_b = Square(fill_color=BLUE, fill_opacity=1).move_to(ORIGIN + RIGHT * 5)

        group = Group(square_r, square_g, square_b)

        self.play(FadeIn(group))
        self.wait(1)

        self.play(group.animate.arrange(center=False, last=True, direction=LEFT))

```

If modify `Mobject.arrange()` as I did, you have to specify the `direction` param as `LEFT` when call this method, otherwise the other object in the group will move to the right of the target object (which is assumed to be the rightmost one). Like this:

```python
self.play(group.animate.arrange(center=False, last=True))  # without direction=LEFT
```

https://github.com/user-attachments/assets/62a1595f-1fff-4405-a313-1fdd9396296b

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Select the last object of the group as the alignment target when using `Mobject.arrange()` #4183

Description of proposed feature

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How can the new feature be used?

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	for m1, m2 in zip(self.submobjects, self.submobjects[1:]):
	m2.next_to(m1, direction, buff, **kwargs)
	if center:
	self.center()
	return self

Select the last object of the group as the alignment target when using Mobject.arrange() #4183

Description

Description of proposed feature

My motivation

Why

How can the new feature be used?

Additional comments

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

Select the last object of the group as the alignment target when using `Mobject.arrange()` #4183