patch 9.0.1539: typst filetype is not recognized

Problem:    Typst filetype is not recognized.
Solution:   Distinguish between sql and typst. (Gaetan Lepage, closes #12363)

runtime/autoload/dist/ft.vim

@@ -470,7 +470,7 @@ enddef
 
 # Returns true if file content looks like LambdaProlog module
 def IsLProlog(): bool
-  # skip apparent comments and blank lines, what looks like 
+  # skip apparent comments and blank lines, what looks like
   # LambdaProlog comment may be RAPID header
   var l: number = nextnonblank(1)
   while l > 0 && l < line('$') && getline(l) =~ '^\s*%' # LambdaProlog comment
@@ -1106,6 +1106,31 @@ export def FTlsl()
   endif
 enddef
 
+export def FTtyp()
+  if exists("g:filetype_typ")
+    exe "setf " .. g:filetype_typ
+    return
+  endif
+
+  # Look for SQL type definition syntax
+  for line in getline(1, 200)
+    # SQL type files may define the casing
+    if line =~ '^CASE\s\==\s\=\(SAME\|LOWER\|UPPER\|OPPOSITE\)$'
+      setf sql
+      return
+    endif
+
+    # SQL type files may define some types as follows
+    if line =~ '^TYPE\s.*$'
+      setf sql
+      return
+    endif
+  endfor
+
+  # Otherwise, affect the typst filetype
+  setf typst
+enddef
+
 # Set the filetype of a *.v file to Verilog, V or Cog based on the first 200
 # lines.
 export def FTv()