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/compiler-core/src/utils.ts

@@ -25,7 +25,7 @@ import {
 import { TransformContext } from './transform'
 import {
   MERGE_PROPS,
-  PORTAL,
+  TELEPORT,
   SUSPENSE,
   KEEP_ALIVE,
   BASE_TRANSITION
@@ -38,8 +38,8 @@ export const isBuiltInType = (tag: string, expected: string): boolean =>
   tag === expected || tag === hyphenate(expected)
 
 export function isCoreComponent(tag: string): symbol | void {
-  if (isBuiltInType(tag, 'Portal')) {
-    return PORTAL
+  if (isBuiltInType(tag, 'Teleport')) {
+    return TELEPORT
   } else if (isBuiltInType(tag, 'Suspense')) {
     return SUSPENSE
   } else if (isBuiltInType(tag, 'KeepAlive')) {