Revert "chore: move to tsup"

This reverts commit 65a6aa5fda.

src/utils/index.ts

@@ -0,0 +1,5 @@
+export * from './popper'
+
+export function classNames (...classes: any[string]) {
+  return classes.filter(Boolean).join(' ')
+}

src/utils/popper.ts

@@ -0,0 +1,26 @@
+import { ref, onMounted, watchEffect } from 'vue'
+import { createPopper } from '@popperjs/core'
+
+export function usePopper (options: object) {
+  const reference = ref(null)
+  const popper = ref(null)
+
+  onMounted(() => {
+    watchEffect((onInvalidate) => {
+      if (!popper.value) { return }
+      if (!reference.value) { return }
+
+      const popperEl = popper.value.el || popper.value
+      const referenceEl = reference.value.el || reference.value
+
+      if (!(referenceEl instanceof HTMLElement)) { return }
+      if (!(popperEl instanceof HTMLElement)) { return }
+
+      const { destroy } = createPopper(referenceEl, popperEl, options)
+
+      onInvalidate(destroy)
+    })
+  })
+
+  return [reference, popper]
+}