The template binding API in @angular/compiler exposes information about a
template that is synthesized from the template structure and its scope
(associated directives and pipes).
This commit introduces a new API, `getEntitiesInTemplateScope`, which
accepts a `Template` object (or `null` to indicate the root template) and
returns all `Reference` and `Variable` nodes that are visible at that level
of the template, including those declared in parent templates.
This API is needed by the template type-checker to support autocompletion
APIs for the Language Service.
PR Close#39048