feat(compiler): Add a enableLegacyTemplate option to support <template>

When the `enableLegacyTemplate` is set to `false`, `<template>` tags and the
`template` attribute are no more used to define angular templates but are
treated as regular tag and attribute.

The default value is `true`.

In order to define a template, you have to use the `<ng-template>` tag.

This option applies to your application and all the libraries it uses. That is
you should make sure none of them rely on the legacy way to defined templates
when this option is turned off (`false`).

tools/@angular/tsc-wrapped/src/options.ts

@@ -78,6 +78,9 @@ interface Options extends ts.CompilerOptions {
 
   // Whether to embed debug information in the compiled templates
   debug?: boolean;
+
+  // Whether to enable support for <template> and the template attribute (true by default)
+  enableLegacyTemplate?: boolean;
 }
 
 export default Options;