Rename method named "replace" in Mobject and OpenGLMobject

[GoThrones]

Overview: What does this pull request change?

This PR renames the method named "replace" in mobject.py and opengl_mobject.py, and adds a wrapper with a warning that this method will be deprecated in future.

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

There are 3 methods named replace in manimce source code.
The one in Scene class does what a method named "replace" is expected to do: it replaces the target mobject with the one calling this method.
The 2nd works with strings.
The third one is in mobject.py and in opengl_mobject.py and it works on mobjects only. The method has been renamed to "match_size_and_position_to" because that's what it does. It matches the size and position of the mobject calling it, to the target mobject. The erstwhile name "replace" in mobject.py and opengl_mobject.py is misleading.

Other places in manimce source code, where this replace method of mobject.py and opengl_mobject.py is called, has been kept as it was, for the time being.

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

[behackl]

This is a deprecation and name change that I do support, replace really does mean something completely different, semantically. I'd like to hear what the other devs think about this as well.

Thanks for your contribution(s)!