Fixed text center of rotation for add_fixed_orientation_mobjects()

[vihdutta]

Overview: What does this pull request change?

Modified the fix_orientation function under opengl_mobject.py to fix an error in center of rotation for text objects according to #4644 . The @affects_shader_info_id decorator called fix_orientation once per submobject, so each glyph used its own get_center() as the pivot instead of the whole label’s center. I changed it so that it computes a single anchor from the mobject fix_orientation is called on, then uses that one point for every part of the label (every submobject). This makes it so the whole string spins as a single unit around the text's real middle.

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

Bugfix.

Links to added or changed documentation pages

Added comment under the fix_orientation() function to detail why "@affects_shader_info_id" is not being used from this PR (since the surrounding functions use it).

Further Information and Comments

Showing the text rotation works properly given the reproduction code/example from issue #4644

This was also ran on the OpenGL renderer (like #4644 ) but on Windows 11.

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