Ensure consistent size of form fields regardless of label position

packages/standard-components/src/forms/FieldGroup.svelte

@@ -9,9 +9,9 @@
 </script>
 
 <div use:styleable={$component.styles}>
-  <form
+  <div
     class="spectrum-Form"
     class:spectrum-Form--labelsAbove={labelPosition === 'above'}>
     <slot />
-  </form>
+  </div>
 </div>

packages/standard-components/src/forms/SpectrumField.svelte

@@ -56,6 +56,10 @@
 </FieldGroupFallback>
 
 <style>
+  .spectrum-Form-itemField {
+    width: 360px;
+  }
+
   .error {
     color: var(
       --spectrum-semantic-negative-color-default,