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/runtime-core/src/index.ts

@@ -53,7 +53,7 @@ export {
 } from './vnode'
 // Internal Components
 export { Text, Comment, Fragment } from './vnode'
-export { Portal, PortalProps } from './components/Portal'
+export { Teleport, TeleportProps } from './components/Teleport'
 export { Suspense, SuspenseProps } from './components/Suspense'
 export { KeepAlive, KeepAliveProps } from './components/KeepAlive'
 export {