Fix #12359: Reset min-width on fieldsets so that they don't break responsive...

Fix #12359: Reset min-width on fieldsets so that they don't break responsive tables and behave more like standard block level elements

dist/css/bootstrap.css

@@ -1617,6 +1617,7 @@ table th[class*="col-"] {
   }
 }
 fieldset {
+  min-width: 0;
   padding: 0;
   margin: 0;
   border: 0;

less/forms.less

@@ -11,6 +11,10 @@ fieldset {
   padding: 0;
   margin: 0;
   border: 0;
+  // Chrome and Firefox set a `min-width: -webkit-min-content;` on fieldsets,
+  // so we reset that to ensure it behaves more like a standard block element.
+  // See https://github.com/twbs/bootstrap/issues/12359.
+  min-width: 0;
 }
 
 legend {