Umm... what are you even talking about?
Go has had templating built into the standard library since... forever?
And Go templates can use other templates, as long as they're all loaded into the same context, if that's what you were getting at.
simple examples of Go's built-in templates: https://gowebexamples.com/templates/
templates using other templates: https://levelup.gitconnected.com/using-go-templates-for-effe...