Fix #3548: Match MathTex subscripts/superscripts by position

[Nikhil172913832]

Overview: What does this pull request change?

Fixes issue where MathTex submobjects did not correctly correspond to their tex_strings when using subscripts and superscripts in different orders. The fix uses geometric position matching specifically for script elements (^, _) to handle LaTeX's reordering while preserving sequential matching for non-script elements.

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

Problem: LaTeX compiles expressions like A ^n _1 and A _1 ^n to identical SVG output where subscripts and superscripts may appear in a different order than specified. This caused MathTex('A', '^n', '_1') and MathTex('A', '_1', '^n') to have submobjects that didn't match their original tex_strings, breaking operations like get_parts_by_tex() and set_color_by_tex().

Solution: Modified _break_up_by_substrings() method to detect script elements (tex strings starting with ^ or _) and match them to rendered submobjects based on geometric position (center point). Non-script elements continue using sequential matching to maintain backward compatibility and avoid issues with complex formulas.

Impact: Users can now reliably access and manipulate subscripts/superscripts by their tex strings regardless of the order they're specified.

Links to added or changed documentation pages

No documentation changes required.

Further Information and Comments

• Fixes Rendered submobjects of MathTex may not correspond to their tex strings #3548
• All existing tests pass (20/20 in test_texmobject.py)
• Added regression test: test_tex_strings_with_subscripts_and_superscripts()

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