wp-includes/class-wp-customize-manager.php:2277Retrieves the template name of the previewed theme.
string public function get_template() { return $this->theme()->get_template(); }Introduced in 3.4.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-customize-manager.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.