patch 9.1.0635: filetype: SuperHTML template files not recognized

Problem:  filetype: SuperHTML template files not recognized
Solution: Update the filetype detection code to detect '*.shtml' either
          as HTML (Server Side Includes) or SuperHTML (template files)
          (EliSauder)

related: #15355
related: #15367

Signed-off-by: EliSauder <24995216+EliSauder@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/autoload/dist/ft.vim b/runtime/autoload/dist/ft.vim
index e53cdac..c8942eb 100644
--- a/runtime/autoload/dist/ft.vim
+++ b/runtime/autoload/dist/ft.vim
@@ -421,7 +421,6 @@
       setf htmlangular
       return
     endif
-
     # Check for XHTML
     if getline(n) =~ '\<DTD\s\+XHTML\s'
       setf xhtml
@@ -432,6 +431,11 @@
       setf htmldjango
       return
     endif
+    # Check for SuperHTML
+    if getline(n) =~ '<extend\|<super>'
+        setf superhtml
+        return
+    endif
     n += 1
   endwhile
   setf FALLBACK html
diff --git a/runtime/filetype.vim b/runtime/filetype.vim
index d028265..bdf591a 100644
--- a/runtime/filetype.vim
+++ b/runtime/filetype.vim
@@ -1039,7 +1039,7 @@
 " Translate shell
 au BufNewFile,BufRead init.trans,*/etc/translate-shell,.trans	setf clojure
 
-" HTML (.shtml and .stm for server side)
+" HTML (.stm for server side, .shtml is server-side or superhtml)
 au BufNewFile,BufRead *.html,*.htm,*.shtml,*.stm  call dist#ft#FThtml()
 au BufNewFile,BufRead *.cshtml			setf html