Rewrite VMobject subpath getters by calculating split indices

[chopan050]

Overview: What does this pull request change?

Related PR: #3292

Taking inspiration from ManimGL, I added new methods VMobject.get_subpath_split_indices() and VMobject.get_subpath_split_indices_from_points(), which instead of explicitly obtaining a Python list of subpaths, it obtains an (n_subpaths, 2) ndarray of indices indicating where every subpath starts and ends.

These methods also accept parameters n_dims (which allows us to choose between 2D or 3D point comparison) and strip_null_end_curves (useful in a future PR for VMobject.align_points(), where the null end curves at every subpath must be removed as a fix to certain bug).

Then I rewrote VMobject.get_subpaths_from_points() and VMobject.gen_subpaths_from_points_2d() to use this new method VMobject.get_subpath_split_indices_from_points().

TODO: vectorize VMobject.consider_points_equals() in a subsequent PR for extra optimization in VMobject.get_subpath_split_indices_from_points().

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

Methods like VMobject.change_anchor_mode() and VMobject.align_points() could benefit from calculating split indices, since they allow for things such as calculating the lengths of the subpaths in a vectorized fashion, which then allows for creating a single NumPy empty array with the right length from the beginning, rather than appending into a NumPy array.

Links to added or changed documentation pages

Further Information and Comments

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