Added cubic bézier bounding box calculation to width/height attribute :class:.VMobject

[jsonvillanueva]

Overview: What does this pull request change?

Widths and heights of :class:.VMobject no longer simply use its control points handles to calculate the bounding box.

It also removes some dead code related to cubic bezier curves that isn't used in VMobject (simplifying it) and moves some logic specific to the Cubic Bezier out of VMobject.

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

Closes #3619

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

[MrDiver]

Is this ready for review?
Do we need to update the test?

[behackl]

Judging from the CI output some more work is required here; I'll mark this as a draft.