Refactor/put start and end on

[GoThrones]

Overview: What does this pull request change?

This PR refactors the method "put_start_and_end_on" in mobject.py and opengl_mobject.py:

Replaces self.points = np.array(start) with self.shift(np.asarray(start) - current_start) in the case of a mobject whose start and end point are the same, in both mobject.py and opengl_mobject.py

Adds a warning that warns the user that the mobject which is calling this method is a loop, and it will be shifted.

Some variable names have been changed for better reading.

Motivation and Explanation: Why and how do your changes improve the library?

The put_start_and_end_on method in both mobject.py and opengl_mobject.py previously used self.points = np.array(start) when the mobject had its start and end as the same point. This collapsed all of the mobject's points into a single Point3D, destroying its geometry entirely. For example, calling this method on a Circle or Square would reduce it to a single point, making it cease to exist visually.
This PR fixes the issue by replacing that line with self.shift(np.asarray(start) - current_start), which simply repositions the mobject to the start point while fully preserving its geometry.

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested