Add_tip shifts the line

Nobody has claimed this yet.

## Description of bug / unexpected behavior

I wanted to use a tikz-equivalent of `-|` in manim to simply write the equivalent of the tikz code:
```
\draw[rounded corners,-Stealth] (0,0) -| (1,-1);
```
to obtain something like

but it turned out that the equivalent manim code is a huge mess:

```
import manim.mobject.geometry.tips as tips
class ellbowarrow(Scene):
def construct(self):
def add_tip(
line,
shorten=True,
tip_shape: type[tips.ArrowTip] | None = None,
tip_length: float | None = None,
tip_width: float | None = None,
):
tip = line.get_unpositioned_tip(
tip_length=tip_length,
tip_shape = tip_shape,
tip_width = tip_width,
)
tipangle = Line(tip.base, tip.tip_point).get_angle()
angle = Line(line.point_from_proportion(0.999),line.point_from_proportion(1.0)).get_angle()
tip.rotate(angle-tipangle,about_point=tip.base)
tip.shift(line.get_end()-tip.tip_point)
if shorten==True:
points = line.get_all_points()
points[-1]=tip.base
line.set_points(points)
line.add(tip)
return line
Line.add_tip = add_tip

grid = NumberPlane().add_coordinates()
self.add(grid)

p1 = Dot([-4,2,0],color=RED)
p2 = Dot([4,-1,0],color=BLUE)

c1 = Dot(p1.get_center()*UP+p2.get_center()*RIGHT-0.5*RIGHT, color=YELLOW)
c2 = Dot(p2.get_center()*RIGHT+p1.get_center()*UP-0.5*UP, color=TEAL)
self.add(p1,p2,c1,c2)
line1 = Line().set_points_as_corners(
[p1.get_center(), p1.get_center()*UP+p2.get_center()*RIGHT-0.5*RIGHT]
)
line1.add_cubic_bezier_curve(
p1.get_center()*UP+p2.get_center()*RIGHT-0.5*RIGHT,
p2.get_center()*RIGHT+p1.get_center()*UP,
p2.get_center()*RIGHT+p1.get_center()*UP,
p2.get_center()*RIGHT+p1.get_center()*UP-.5*UP
)
line1.add_line_to(p2.get_center())
line1.add_tip(shorten=False, tip_length=0.5)

self.play(Create(line1))
self.wait()
```

(thanks uwezi for the help)

One issue is the lack of `rounded corners` (see https://github.com/ManimCommunity/manim/issues/4443), but the other issue is that `Line.add_tip` is broken as discussed in https://discord.com/channels/581738731934056449/1370706466541011055/1370728872416514141:

Indeed, the naive code:
```
from manim import *

class Terminology(Scene):
def construct(self):
# Grid
grid = NumberPlane()
grid.add_coordinates()
self.add(grid)

plainText = Text("Plaintext", font_size=30, color=YELLOW)
plainText.to_edge(LEFT, buff=0.8)
plainTextRect = SurroundingRectangle(plainText, color=YELLOW, buff=0.3)

self.play(Write(plainText))
self.play(Write(plainTextRect))

encryptionAlgorithm = Text("Encryption\nAlgorithm", font_size=30, color=BLUE)
encryptionAlgorithm.move_to(UP*2)
encryptionAlgorithmRect = SurroundingRectangle(encryptionAlgorithm, color=BLUE)
self.play(Write(encryptionAlgorithm))
self.play(Write(encryptionAlgorithmRect))

line1 = Line()
line1.set_points_as_corners([
plainTextRect.get_top(),
[plainTextRect.get_center()[0], 2, 0],
encryptionAlgorithmRect.get_left()
]).add_tip(tip_length=0.15)

self.play(Write(line1))

cipher = Text("Cipher", font_size=30, color=RED)
cipher.to_edge(RIGHT, buff=0.8)
cipherRect = SurroundingRectangle(cipher, color=RED, buff=0.3)

line2 = Line()
line2.set_points_as_corners([
encryptionAlgorithmRect.get_right(),
[cipherRect.get_center()[0], 2, 0],
cipherRect.get_top()
]).add_tip(tip_length=0.15)

self.play(Write(line2))

self.play(Write(cipher))
self.play(Write(cipherRect))

self.wait()
```
produces

Reproduce the multi-segment Line example and inspect manim.mobject.geometry.tips together with Line.add_tip, focusing on how the tip is positioned and how the line points are shortened. The fix is complete when adding a tip does not shift the line unexpectedly and the arrowhead remains aligned with the final segment in the demonstrated cases.

Written by the indexing model from the issue text.