fix(InputMenu): emit focus event (#2386)

Co-authored-by: Benjamin Canac <canacb1@gmail.com>

docs/app/components/content/examples/input-menu/InputMenuOpenFocusExample.vue

@@ -0,0 +1,14 @@
+<script setup lang="ts">
+const open = ref(false)
+const items = ref(['Backlog', 'Todo', 'In Progress', 'Done'])
+const selected = ref('Backlog')
+</script>
+
+<template>
+  <UInputMenu
+    v-model="selected"
+    v-model:open="open"
+    :items="items"
+    @focus="open = true"
+  />
+</template>