feat: `useModal()` slots allow passing components directly

[Mini-ghost]

In current, useModal usage like following code:

<script setup lang="ts">
import { markRaw } from 'vue'
import { VueFinalModal, useModal } from 'vue-final-modal'

const modalInstance = useModal({
  component: markRaw(VueFinalModal),
  slots: {
    // pass a html string
    default: '<p>The content of the modal</p>',

    // pass a object include `component` and optional `attrs`
    default: {
      component: markRaw(CustomComponent),
      attrs: {
        // <CustomComponent />'s  props
      }
    }
  }
})
</script>

This PR improves two features:

1. Users no longer need to use markRaw to wrapper component.
2. slots allow passing slot name and components directly.

The following code is new usage after this PR

<script setup lang="ts">
import { markRaw } from 'vue'
import { VueFinalModal, useModal } from 'vue-final-modal'

const modalInstance = useModal({
  component: VueFinalModal,
  slots: {
    // pass a html string
    default: '<p>The content of the modal</p>',

    // pass a object include `component` and optional `attrs`
    default: {
      component: CustomComponent,
      attrs: {
        // <CustomComponent />'s  props
      }
    },

    // pass a component directly
    default: CustomComponent,
  }
})
</script>