hugolib: Add .Name as a shortcode variable

Fixes #5546

content/en/variables/shortcodes.md

@@ -20,6 +20,9 @@ toc: false
 
 [Shortcodes][shortcodes] have access to parameters delimited in the shortcode declaration via [`.Get`][getfunction], page- and site-level variables, and also the following shortcode-specific fields:
 
+.Name
+: Shortcode name.
+
 .Ordinal
 : Zero-based ordinal in relation to its parent. If the parent is the page itself, this ordinal will represent the position of this shortcode in the page content.