模板中每个ng-template，会触发函数ɵɵtemplate：
ɵɵtemplate里会自动创建一个comment element，通过方法createComment完成：
ɵɵtemplate函数内部会创建一个comment element.
/**
* Creates an LContainer for an ng-template (dynamically-inserted view), e.g.
*
* <ng-template #foo>
* <div></div>
* </ng-template>
*
* @param index The index of the container in the data array
* @param templateFn Inline template
* @param decls The number of nodes, local refs, and pipes for this template
* @param vars The number of bindings for this template
* @param tagName The name of the container element, if applicable
* @param attrsIndex Index of template attributes in the `consts` array.
* @param localRefs Index of the local references in the `consts` array.
* @param localRefExtractor A function which extracts local-refs values from the template.
* Defaults to the current element associated with the local-ref.
*
* @codeGenApi
*/
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