[IMP] component tags: allow injecting values in xml tag string

With this commit, we can now do this:

      const SUBTEMPLATE = xml`<span><t t-esc="state.n"/></span>`
      class Parent extends Widget {
          static template = xml`<div><t t-call="${SUBTEMPLATE}"/></div>`
          state = {n: 42};
      }

tests/component/__snapshots__/component.test.ts.snap

@@ -1068,6 +1068,24 @@ exports[`other directives with t-component t-on with stop and/or prevent modifie
 }"
 `;
 
+exports[`random stuff/miscellaneous can inject values in tagged templates 1`] = `
+"function anonymous(context,extra
+) {
+    var h = this.h;
+    let c1 = [], p1 = {key:1};
+    var vn1 = h('div', p1, c1);
+    result = vn1;
+    let c2 = [], p2 = {key:2};
+    var vn2 = h('span', p2, c2);
+    c1.push(vn2);
+    var _3 = context['state'].n;
+    if (_3 || _3 === 0) {
+        c2.push({text: _3});
+    }
+    return vn1;
+}"
+`;
+
 exports[`random stuff/miscellaneous snapshotting compiled code 1`] = `
 "function anonymous(context,extra
 ) {

tests/component/component.test.ts

@@ -2310,6 +2310,19 @@ describe("random stuff/miscellaneous", () => {
       "C:patched"
     ]);
   });
+
+  test("can inject values in tagged templates", async () => {
+      const SUBTEMPLATE = xml`<span><t t-esc="state.n"/></span>`
+      class Parent extends Widget {
+          static template = xml`<div><t t-call="${SUBTEMPLATE}"/></div>`
+          state = {n: 42};
+      }
+
+    const widget = new Parent(env);
+    await widget.mount(fixture);
+    expect(env.qweb.templates[Parent.template].fn.toString()).toMatchSnapshot();
+    expect(fixture.innerHTML).toBe('<div><span>42</span></div>')
+  });
 });
 
 describe("async rendering", () => {