patch 9.0.0935: when using dash it may not be recognize as filetype "sh"

Problem:    When using dash it may not be recognize as filetype "sh".
Solution:   Add checks for "dash". (Eisuke Kawashima,closes #11600)

runtime/autoload/dist/ft.vim

@@ -712,7 +712,8 @@ export def SetFileTypeSH(name: string)
     if exists("b:is_sh")
       unlet b:is_sh
     endif
-  elseif name =~ '\<sh\>'
+  elseif name =~ '\<sh\>' || name =~ '\<dash\>'
+    # Ubuntu links "sh" to "dash", thus it is expected to work the same way
     b:is_sh = 1
     if exists("b:is_kornshell")
       unlet b:is_kornshell

runtime/autoload/dist/script.vim

@@ -53,8 +53,8 @@ def DetectFromHashBang(firstline: string)
     name = 'wish'
   endif
 
-  # Bourne-like shell scripts: bash bash2 ksh ksh93 sh
-  if name =~ '^\(bash\d*\|\|ksh\d*\|sh\)\>'
+    # Bourne-like shell scripts: bash bash2 dash ksh ksh93 sh
+  if name =~ '^\(bash\d*\|dash\|ksh\d*\|sh\)\>'
     call dist#ft#SetFileTypeSH(line1)
 
     # csh scripts