[IMP] portal: add support for .closest modifier

It is sometimes useful in practice to be able to configure the portal so
that it looks for a target as close as possible as the portal location.
For example, in odoo, a portal may be set up in a form view that should
target the current form view. But if the form view itself is in a
dialog, it may fail, because it may find a valid target in the form view that is located
underneath.

With this commit, we add a .closest modifier to the `t-portal`
directive.

tests/compiler/parser.test.ts

@@ -1998,6 +1998,7 @@ describe("qweb parser", () => {
   test("t-portal", async () => {
     expect(parse(`<t t-portal="target">Content</t>`)).toEqual({
       type: ASTType.TPortal,
+      isClosest: false,
       target: "target",
       content: { type: ASTType.Text, value: "Content" },
     });
@@ -2008,6 +2009,7 @@ describe("qweb parser", () => {
       condition: "condition",
       content: {
         content: { type: ASTType.Text, value: "Content" },
+        isClosest: false,
         target: "target",
         type: ASTType.TPortal,
       },
@@ -2016,4 +2018,13 @@ describe("qweb parser", () => {
       type: ASTType.TIf,
     });
   });
+
+  test("t-portal with .closest", async () => {
+    expect(parse(`<t t-portal.closest="target">Content</t>`)).toEqual({
+      type: ASTType.TPortal,
+      isClosest: true,
+      target: "target",
+      content: { type: ASTType.Text, value: "Content" },
+    });
+  });
 });