feat(Slideover): open programmatically (#1465)

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

docs/components/content/examples/SlideoverExampleComposable.vue

@@ -0,0 +1,16 @@
+<script setup lang="ts">
+import { SlideoverExampleComponent } from '#components'
+const slideover = useSlideover()
+const count = ref(0)
+function openSlideover () {
+  count.value += 1
+  slideover.open(SlideoverExampleComponent, {
+    count: count.value,
+    onClose: slideover.close
+  })
+}
+</script>
+
+<template>
+  <UButton label="Reveal slideover" @click="openSlideover" />
+</template>