[IMP] qweb: slightly simplify generated templates

- In some cases, we can simply inline a template key instead of assigning
  it to a variable and then using that variable
- Add component name in generated code for components

src/component/directive.ts

@@ -189,7 +189,7 @@ QWeb.addDirective({
   extraNames: ["props"],
   priority: 100,
   atNodeEncounter({ ctx, value, node, qweb }): boolean {
-    ctx.addLine("//COMPONENT");
+    ctx.addLine(`// Component '${value}'`);
     ctx.rootContext.shouldDefineQWeb = true;
     ctx.rootContext.shouldDefineParent = true;
     ctx.rootContext.shouldDefineUtils = true;

src/qweb/compilation_context.ts

@@ -48,7 +48,10 @@ export class CompilationContext {
    */
   generateTemplateKey(): string {
     const id = this.generateID();
-    let locationExpr = `\`__${this.generateID()}__`;
+    if (this.loopNumber === 0 && !this.currentKey) {
+      return `'__${id}__'`;
+    }
+    let locationExpr = `\`__${id}__`;
     for (let i = 0; i < this.loopNumber - 1; i++) {
       locationExpr += `\${i${i + 1}}__`;
     }