Allow stretched character to increase column size (e.g., if it has minsize). (mathjax/MathJax#3423)

[dpvc]

This PR fixes a problem where the column width for a column with stretchy characters isn't adjusted if the stretched version of the character is wider than the expected stretch width. This can happen if a fixed-size character is used that is slightly larger than needed (which is allowed), or if the stretchy has a minsize attribute that makes it larger than expected. The latter is true in the case cited in mathjax/MathJax#3423.

We fix the problem by making sure we always stretch characters, even if there is only one stretchy (so as to handle midsize even on a single row), and testing if the new width is wider than the column width, and adjusting that width if so. We also remove a variable that is no longer needed.

A test case is

\begin{CD}
A @= B
\end{CD}

Without this patch the equal sign overlaps the A and B.

Resolves issue mathjax/MathJax#3423.

[codecov]

Codecov Report

❌ Patch coverage is 14.28571% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.71%. Comparing base (afaf1ea) to head (2bde9c8).

Files with missing lines	Patch %	Lines
ts/output/common/Wrappers/mtable.ts	14.28%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1353      +/-   ##
===========================================
- Coverage    86.72%   86.71%   -0.01%     
===========================================
  Files          337      337              
  Lines        84145    84149       +4     
  Branches      3140     3140              
===========================================
- Hits         72971    72970       -1     
- Misses       11174    11179       +5     

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