patch 8.2.3703: most people call F# "fsharp" and not "fs"

Problem:    Most people call F# "fsharp" and not "fs".
Solution:   Rename filetype "fs" to "fsharp".
diff --git a/runtime/autoload/dist/ft.vim b/runtime/autoload/dist/ft.vim
index 0cbcb1b..74df871 100644
--- a/runtime/autoload/dist/ft.vim
+++ b/runtime/autoload/dist/ft.vim
@@ -231,7 +231,7 @@
 	  \ || line =~ '^\s*: \S'
       setf forth
     else
-      setf fs
+      setf fsharp
     endif
   endif
 endfunc
diff --git a/runtime/filetype.vim b/runtime/filetype.vim
index fd3998b..f687cc7 100644
--- a/runtime/filetype.vim
+++ b/runtime/filetype.vim
@@ -634,9 +634,6 @@
 " Forth
 au BufNewFile,BufRead *.ft,*.fth		setf forth
 
-" F# or Forth
-au BufNewFile,BufRead *.fs			call dist#ft#FTfs()
-
 " Reva Forth
 au BufNewFile,BufRead *.frt			setf reva
 
@@ -652,6 +649,12 @@
 " FStab
 au BufNewFile,BufRead fstab,mtab		setf fstab
 
+" F# or Forth
+au BufNewFile,BufRead *.fs			call dist#ft#FTfs()
+
+" F#
+au BufNewFile,BufRead *.fsi,*.fsx		setf fsharp
+
 " GDB command files
 au BufNewFile,BufRead .gdbinit,gdbinit		setf gdb