Merge pull request #1347 from mathjax/issue3429

Don't use padding for horizontal stretchy extenders.  (mathjax/MathJax#3429)

Author: dpvc

ts/output/chtml/FontData.ts

@@ -583,6 +583,9 @@ export class ChtmlFontData extends FontData<
       padding: this.padding(HDW as ChtmlCharData, w - HDW[2]),
     };
     if (part === 'ext') {
+      const padding = (css.padding as string).split(/ /);
+      padding[1] = padding[3] = '0';
+      css.padding = padding.join(' ');
       if (!w && options.dx) {
         w = 2 * options.dx - 0.06;
       }