[FIX] qweb: add support for t-att-value on textareas

The code did not treat textareas in the same way as inputs. As a result,
using t-att-value on a textarea did not work.

closes #872

src/qweb/qweb.ts

@@ -705,7 +705,7 @@ export class QWeb extends EventBus {
           isProp = key === "selected" || key === "disabled";
           break;
         case "textarea":
-          isProp = key === "readonly" || key === "disabled";
+          isProp = key === "readonly" || key === "disabled" || key === "value";
           break;
         case "button":
         case "select":

tests/qweb/qweb.test.ts

@@ -1931,6 +1931,25 @@ describe("special cases for some specific html attributes/properties", () => {
     let elm = vnode2.elm as HTMLInputElement;
     expect(elm.indeterminate).toBe(true);
   });
+
+  test("textarea with t-att-value", () => {
+    // render input with initial value
+    qweb.addTemplate("test", `<textarea  t-att-value="v"/>`);
+    const vnode1 = qweb.render("test", { v: "zucchini" });
+    const vnode2 = patch(document.createElement("textarea"), vnode1);
+    let elm = vnode2.elm as HTMLInputElement;
+    expect(elm.value).toBe("zucchini");
+
+    // change value manually in textarea, to simulate user textarea
+    elm.value = "tomato";
+    expect(elm.value).toBe("tomato");
+
+    // rerender with a different value, and patch actual dom, to check that
+    // textarea value was properly reset by owl
+    const vnode3 = qweb.render("test", { v: "potato" });
+    patch(vnode2, vnode3);
+    expect(elm.value).toBe("potato");
+  });
 });
 
 describe("whitespace handling", () => {