'forms-inline' class should ensure all direct descendants are inline

This is a followup from #3224958: Olivero should style Views exposed filters as inline (currently are stacked)/

Within Olivero we're adding the following code which ensures that all direct descendants will be inline (which is the expectation when setting that CSS class)

.form--inline > * {
   display: inline-block;
   margin-top: 0.5625rem;
   margin-bottom: 0;
   vertical-align: top; /* Ensure proper alignment if description is present. */
 }

We should do this within all of Drupal core, as it's a more robust solution rather than relying on the child elements CSS class.