fix(stepper): make the stepper stretch to its parent size (#12902)

Co-authored-by: viktorkombov <[email protected]>
Co-authored-by: Simeon Simeonoff <[email protected]>

Author: 3 people

projects/igniteui-angular/src/lib/core/styles/components/stepper/_stepper-theme.scss

@@ -382,10 +382,13 @@
         white-space: nowrap;
         flex-direction: column;
         width: 100%;
+        flex: none;
     }
 
     %igx-stepper__body {
-        position: relative
+        position: relative;
+        flex-direction: column;
+        flex: 1 1 auto;
     }
 
     %stepper-display,