feat(Modal): add prevent-close prop

Resolves #303

docs/components/content/examples/ModalExampleDisableTransition.vue

@@ -0,0 +1,15 @@
+<script setup>
+const isOpen = ref(false)
+</script>
+
+<template>
+  <div>
+    <UButton label="Open" @click="isOpen = true" />
+
+    <UModal v-model="isOpen" :transition="false">
+      <div class="p-4">
+        <Placeholder class="h-48" />
+      </div>
+    </UModal>
+  </div>
+</template>