fix(input): space following default placeholderClass should be trimmed

Author: b2nil

src/components/input/index.ts

@@ -149,7 +149,10 @@ const AtInput = defineComponent({
       'at-input__overlay--hidden': !inputProps.value.disabled
     }))
 
-    const placeholderClasses = computed(() => `placeholder ${props.placeholderClass}`)
+    const placeholderClasses = computed(() => ({
+      'placeholder': true,
+      [`${props.placeholderClass}`]: Boolean(props.placeholderClass)
+    }))
 
     const titleClasses = computed(() => ({
       'at-input__title': true,