patch 8.2.1437: Vim9: 'statusline' is evaluated using Vim9 script syntax

Problem:    Vim9: 'statusline' is evaluated using Vim9 script syntax.
Solution:   Always use legacy script syntax.

src/eval.c

@@ -520,6 +520,7 @@ eval_to_string(
 /*
  * Call eval_to_string() without using current local variables and using
  * textwinlock.  When "use_sandbox" is TRUE use the sandbox.
+ * Use legacy Vim script syntax.
  */
     char_u *
 eval_to_string_safe(
@@ -528,7 +529,9 @@ eval_to_string_safe(
 {
     char_u	*retval;
     funccal_entry_T funccal_entry;
+    int		save_sc_version = current_sctx.sc_version;
 
+    current_sctx.sc_version = 1;
     save_funccal(&funccal_entry);
     if (use_sandbox)
 	++sandbox;
@@ -538,6 +541,7 @@ eval_to_string_safe(
 	--sandbox;
     --textwinlock;
     restore_funccal();
+    current_sctx.sc_version = save_sc_version;
     return retval;
 }
 

src/testdir/test_vim9_script.vim

@@ -1086,6 +1086,20 @@ def Test_cexpr_vimscript()
   set errorformat&
 enddef
 
+def Test_statusline_syntax()
+  # legacy syntax is used for 'statusline'
+  let lines =<< trim END
+      vim9script
+      func g:Status()
+        return '%{"x" is# "x"}'
+      endfunc
+      set laststatus=2 statusline=%!Status()
+      redrawstatus
+      set laststatus statusline= 
+  END
+  CheckScriptSuccess(lines)
+enddef
+
 def Test_list_vimscript()
   # checks line continuation and comments
   let lines =<< trim END

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1437,
 /**/
     1436,
 /**/