[IMP] portal: portal as a Directive

Before this commit, portal was a Component, now is a directive.
This commit also clean some unused code, and fix an issue on the clean
optimization when a portal is found in a condition or a loop.

src/portal.ts

@@ -1,10 +1,8 @@
-import { xml } from "./app/template_set";
 import { BDom, text, VNode } from "./blockdom";
-import { Component } from "./component/component";
 
 const VText: any = text("").constructor;
 
-class VPortal extends VText implements Partial<VNode<VPortal>> {
+export class VPortal extends VText implements Partial<VNode<VPortal>> {
   //   selector: string;
   realBDom: BDom | null;
   target: HTMLElement | null = null;
@@ -49,19 +47,3 @@ class VPortal extends VText implements Partial<VNode<VPortal>> {
     }
   }
 }
-
-export class Portal extends Component {
-  static template = xml`<t t-slot="default"/>`;
-  static props = {
-    target: {
-      type: String,
-    },
-    slots: true,
-  };
-
-  setup() {
-    const node = this.__owl__;
-    const renderFn = node.renderFn;
-    node.renderFn = () => new VPortal(this.props.target, renderFn());
-  }
-}