refactor: rename <portal> to <teleport>

BREAKING CHANGE: `<portal>` has been renamed to `<teleport>`.

    `target` prop is also renmaed to `to`, so the new usage will be:

    ```html
    <Teleport to="#modal-layer" :disabled="isMobile">
      <div class="modal">
        hello
      </div>
    </Teleport>
    ```

    The primary reason for the renaming is to avoid potential naming
    conflict with [native portals](https://wicg.github.io/portals/).

packages/server-renderer/src/index.ts

@@ -13,7 +13,7 @@ export {
 } from './helpers/ssrRenderAttrs'
 export { ssrInterpolate } from './helpers/ssrInterpolate'
 export { ssrRenderList } from './helpers/ssrRenderList'
-export { ssrRenderPortal } from './helpers/ssrRenderPortal'
+export { ssrRenderTeleport } from './helpers/ssrRenderTeleport'
 export { ssrRenderSuspense } from './helpers/ssrRenderSuspense'
 
 // v-model helpers