Removed multiple arrow heads with DashedVMobject

[CobaltIII]

Overview: What does this pull request change?

When a DashedVMobject is made, the arrow is duplicated and overlayed for every segment or 'dash'. This change makes it so that only one arrowhead is seen during it all. Fixes #3220 . Also makes the TipableVMobject.pop_tips() function more robust if we enter an object that does not have any tips on either side.

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

It fixes an issue I found on the issues tab. I think it makes the usage of dashed arrows and vectors easier and more aesthetically pleasing.

Links to added or changed documentation pages

Further Information and Comments

Fixes the issue given here #3220.

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

[OliverStrait]

Hi, thank you for searching the cause of tip duplication.

• Fixes the linked issue with this result

[CobaltIII]

@OliverStrait The tests were passing however in the last commit to the main branch, the readthedocs test wasn't conducted and it is creating an issue by making a string of color "#CCC>" which doesn't exist. The previous commits were fine and all were passing. I noticed this issue with a few other pull requests as well.