patch 8.2.4238: *.tf file could be fileytpe "tf" or "terraform"

Problem:    *.tf file could be fileytpe "tf" or "terraform".
Solution:   Detect the type from the file contents. (closes #9642)

src/testdir/test_filetype.vim

@@ -771,6 +771,24 @@ func Test_hook_file()
   filetype off
 endfunc
 
+func Test_tf_file()
+  filetype on
+
+  call writefile([';;; TF MUD client is super duper cool'], 'Xfile.tf')
+  split Xfile.tf
+  call assert_equal('tf', &filetype)
+  bwipe!
+
+  call writefile(['provider "azurerm" {'], 'Xfile.tf')
+  split Xfile.tf
+  call assert_equal('terraform', &filetype)
+  bwipe!
+
+  call delete('Xfile.tf')
+  filetype off
+endfunc
+
+
 func Test_ts_file()
   filetype on
 

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4238,
 /**/
     4237,
 /**/