[FIX] qweb: bind handlers to component

Before this commit, the handlers were bound to the current context,
which is often the component but not necessarily.  In some cases, a sub
scope can be created (with t-foreach, or slots, or t-call), and the
context is actually an object with the actual component instance it its
prototype chain, but not the component.

src/qweb/extensions.ts

@@ -55,13 +55,15 @@ export function makeHandlerCode(
 
   // then generate code
   if (isMethodCall) {
+    ctx.rootContext.shouldDefineUtils = true;
+    const comp = `utils.getComponent(context)`;
     if (args) {
       let argId = ctx.generateID();
       ctx.addLine(`let args${argId} = [${ctx.formatExpression(args)}];`);
-      code = `context['${name}'](...args${argId}, e);`;
+      code = `${comp}['${name}'](...args${argId}, e);`;
       putInCache = false;
     } else {
-      code = `context['${name}'](e);`;
+      code = `${comp}['${name}'](e);`;
     }
   } else {
     // if we get here, then it is an expression